System and method for joint resurface repair

ABSTRACT

A generic bone implant, or set of standardized implants, is created based on using a guide device to develop an axis normal to an articular surface of bone and collecting only one or two data points. A generic cutting tool is used to cut the bone to a point where a generic implant can be used. Several improved tools relating to the procedure for using such an implant, as well as methods for using implants consistent with the invention are further described, including: single-axis and biaxial drill guide tools and methods, generic single-axis implant methods and devices, generic biaxial implant methods and devices, tools and methods for holding or delivering an implant, removal or revision tools and methods, digital measuring systems and methods, and set of measuring gauges for determining the appropriate implant dimensions.

This application is a continuation of U.S. application Ser. No.12/415,503 filed Mar. 31, 2009, now U.S. Pat. No. 7,857,817 issued Dec.28, 2010 which is a continuation of U.S. application Ser. No. 10/618,887filed Jul. 14, 2003, now U.S. Pat. No. 7,510,558 issued Mar. 31, 2009which is a divisional of U.S. application Ser. No. 10/024,077, filedDec. 17, 2001, now U.S. Pat. No. 6,610,067 issued Aug. 26, 2003 which isa continuation-in-part of U.S. application Ser. No. 09/846,657, filedMay 1, 2001, now U.S. Pat. No. 6,520,964 issued Feb. 18, 2003 whichclaims the benefit of U.S. Provisional Application Ser. No. 60/201,049,filed May 1, 2000.

FIELD OF THE INVENTION

This invention relates to devices and methods for the repair of defectsthat occur in articular cartilage on the surface of bones, particularlythe knee.

BACKGROUND OF THE INVENTION

Articular cartilage, found at the ends of articulating bone in the body,is typically composed of hyaline cartilage, which has many uniqueproperties that allow it to function effectively as a smooth andlubricious load-bearing surface. However, when injured, hyalinecartilage cells are not typically replaced by new hyaline cartilagecells. Healing is dependent upon the occurrence of bleeding from theunderlying bone and formation of scar or reparative cartilage calledfibrocartilage. While similar, fibrocartilage does not possess the sameunique aspects of native hyaline cartilage and tends to be far lessdurable.

Hyaline cartilage problems, particularly in knee and hip joints, aregenerally caused by disease such as occurs with rheumatoid arthritis orwear and tear (osteoarthritis), or secondary to an injury, either acute(sudden), or recurrent and chronic (ongoing). Such cartilage disease ordeterioration can compromise the articular surface causing pain andfurther deterioration of joint function. As a result, various methodshave been developed to treat and repair damaged or destroyed articularcartilage.

For smaller defects, traditional options for this type of probleminclude non-operative therapies (e.g., oral medication or medication byinjection into the joint), or performing a surgical procedure calledabrasion arthroplasty or abrasion chondralplasty. The principle behindthis procedure is to attempt to stimulate natural healing. At the defectsite, the bone surface is abraded, removing approximately 1 mm. or lessusing a high-speed rotary burr or shaving device. This creates anexposed subchondral bone bed that will bleed and will initiate afibrocartilage healing response. Although this procedure has been widelyused over the past two decades and can provide good short term results,(1-3 years), the resulting fibrocartilage surface is seldom able tosupport long-term weight bearing, particularly in high-activitypatients, and is prone to wear.

Another procedure, referred to as the “microfracture” technique,incorporates similar concepts of creating exposed subchondral bone.During the procedure, the cartilage layer of the chondral defect isremoved. Several pathways or “microfractures” are created to thesubchondral bleeding bone bed by impacting a metal pick or surgical awlat a minimum number of locations within the lesion. By establishingbleeding in the lesion and by creating a pathway to the subchondralbone, a fibrocartilage healing response is initiated, forming areplacement surface. Results for this technique are generally similar toabrasion chondralplasty.

Another known option to treat damaged articular cartilage is a cartilagetransplant, referred to as a Mosaicplasty or osteoarticular transfersystem (OATS) technique. This involves using a series of dowel cuttinginstruments to harvest a plug of articular cartilage and subchondralbone from a donor site, which can then be implanted into a core madeinto the defect site. By repeating this process, transferring a seriesof plugs, and by placing them in close proximity to one another, inmosaic-like fashion, a new grafted hyaline cartilage surface can beestablished. The result is a hyaline-like surface interposed with afibrocartilage healing response between each graft.

This procedure is technically difficult, as all grafts must be takenwith the axis of the harvesting coring drill being kept perpendicular tothe articular surface at the point of harvest. Also, all graft placementsites must be drilled with the axis of a similar coring tool being keptperpendicular to the articular surface at the point of implantation.Further, all grafts must be placed so that the articular surface portionof these cartilage and bone plugs is delivered to the implantation siteand seated at the same level as the surrounding articular surface. Ifthese plugs are not properly placed in relation to the surroundingarticular surface, the procedure can have a very detrimental effect onthe mating articular surface. If the plugs are placed too far below thelevel of the surrounding articular surface, no benefit from theprocedure will be gained. Further, based on the requirement ofperpendicularity on all harvesting and placement sites, the procedurerequires many access and approach angles that typically require an openfield surgical procedure. Finally, this procedure requires a lengthypost-operative non-weight bearing course.

Transplantation of previously harvested hyaline cartilage cells from thesame patient has been utilized in recent years. After the cartilage isremoved or harvested, it is cultured in the lab to obtain an increase inthe number of cells. These cells are later injected back into the focaldefect site and retained by sewing a patch of periosteal tissue over thetop of the defect to contain the cells while they heal and mature. Thedisadvantages of this procedure are its enormous expense, technicalcomplexity, and the need for an open knee surgery. Further, thistechnique is still considered somewhat experimental and long-termresults are unknown. Some early studies have concluded that thisapproach offers no significant improvement in outcomes over traditionalabrasion and microfracture techniques.

U.S. Pat. No. 5,782,835 to Hart et al. discloses an apparatus and methodfor repair of articular cartilage including a bone plug removal tool,and a bone plug emplacement tool. The method of repairing defectivearticular cartilage includes the steps of removing the defectivecartilage and forming a hole of sufficient depth at the site. A boneplug comprising intact bone and cartilage adhering thereto is removedfrom a bone lacking defective cartilage is placed in the hole at thesite of the damage.

U.S. Pat. No. 5,413,608 to Keller discloses a knee joint endoprosthesisfor replacing the articular surfaces of the tibia comprising a bearingpart which is anchored on the bone having an upper bearing surface and arotatable plateau secured on the bearing surface and forming a part ofthe articular surface to be replaced. A journal rises from the bearingsurface and cooperates with a bore in the plateau to provide lateralsupport.

U.S. Pat. No. 5,632,745 to Schwartz describes a method of surgicallyimplanting into a site a bio-absorbable cartilage repair assembly. Theassembly includes a bio-absorbable polygonal T-shaped delivery unithaving radial ribs to be mounted in the removed area and a porousbio-absorbable insert supported by and in the delivery unit. The methodcomprises the steps of preparing the site to receive the assembly byremoving a portion of the damaged cartilage and preparing the site toreceive the assembly by drilling and countersinking the bone. Theassembly is inserted and seated using an impactor in the drilled andcountersunk hole in the bone until the assembly is flush with thesurrounding articular surface.

U.S. Pat. No. 5,683,466 to Vitale illustrates an articular joint surfacereplacement system having two opposing components. Each component has atapered head piece for covering the end of a bone and for acting as anarticular surface, an integrally formed screw stem of sufficient lengthto extend into the bone and inwardly angled bone grips on the undersideof the head piece to allow fixation to the bone by compression fit. Thepartially spherical convex shaped exterior of the first componentcomplements the partially spherical concave shaped exterior of thesecond component.

U.S. Pat. No. 5,702,401 to Shaffer discloses an intra-articularmeasuring device including a hollow handle defining a first passagewayand a hollow tube having a second passageway extending from the handle,the hollow tube carrying a projection at its distal end for seating on afixed site and a probe disposed at the distal end of the hollow tubewhich may be directed to a second site, to enable measurement of thedistance between the first and second sites.

U.S. Pat. No. 5,771,310 to Vannah describes a method of mapping thethree-dimensional topography of the surface of an object by generatingdigital data points at a plurality of sample points on said surface,each digital data point including a property value and a position valuecorresponding to a particular point representing the properties of thesurface of the object. A 3-D transducer probe (e.g., a digitizer) ismoved on or over the surface along a random path, and the sample pointsare digitized to generate a real-time topography or map on a computerscreen of selected properties of the object, including withoutlimitation, surface elevation, indentation stiffness, elevation ofsub-surface layers and temperature.

Prosthetics for total knee replacement (TKR), whereby the entire kneejoint or a single compartment of the knee joint is replaced can be acommon eventuality for the patient with a large focal defect. Althoughthese patients are also managed with anti-inflammatory medications,eventual erosion of the remaining articular cartilage results ineffusion, pain, and loss of mobility and/or activity for the patient.Problems encountered after implanting such prostheses are usually causedby the eventual loosening of the prosthetic due to osteolysis, wear, ordeterioration of the cements used to attach the device to the hostbones. Further, some prostheses used are actually much larger than thedegenerated tissue that needs to be replaced, so that extensive portionsof healthy bone are typically removed to accommodate the prostheses.Patients who undergo TKR often face a long and difficult rehabilitationperiod, and the life span of the TKR is accepted to be approximately 20years. Accordingly, efforts are made to forgo the TKR procedure for aslong as possible.

Accordingly, there is a need for an improved joint surface replacementsystem that would be effective in restoring a smooth and continuousarticular surface and that would also be as durable as the formerhyaline cartilage surface, within the context of a minimally invasiveprocedure that allows for a nearly immediate return to activity,restoration of lifestyle, and pain relief.

SUMMARY OF THE INVENTION

The present invention provides tools and methods for mapping andmeasuring the articular surface of a joint (or of any bony surface) andfor fabricating a prosthetic device based on this recorded data.

In one method consistent with the invention, once the defect of thechondral surface has been identified, a guide pin is insertedarthroscopically. A fixation screw having a tapered distal tip and anaggressive distal end thread form is then driven into the subchondralbone in relation to a reference axis that is approximately central tothe defect. The fixation device also serves to define a tangent point tothe surrounding articular surface. The screw is driven by a socket typedriver that engages a hex-shaped proximal extension. A furthercylindrical proximal extension of the screw (or other mating feature,e.g., a recess in the screw) that eventually serves as a fixationelement for the surface prosthetic is at this time concealed with acover (or other mating feature corresponding to the mating feature ofthe screw, e.g., a plug for mating with a screw having a recess as itsmating feature) having a radiused proximal end. One or more milled slotsrun the length of the uniform diameter portion of the screw.

Under arthroscopic view, the screw depth is adjusted so that theradiused cover surface is positioned tangent to the radius that definesthe existing articular surface. At this time, the guide pin is removedand the knee is articulated. The depth positioning of the radiused coverestablishes an origin or reference point for all future measuring,cutting, and prosthetic machining operations. Arthroscopic examinationis carried out to confirm positioning.

A measuring tool is inserted on the reference axis. A central element ofthe measuring tool is a static post that establishes the axial locationof origin. By rotating the outer arm or outrigger of the measuring toolrelative to the static post while also maintaining contact with thearticular surface, an axial displacement or Z dimension can beestablished relative to the origin for any point along the known radialsweep of the outrigger to determine the final geometry of the prostheticsurface which fits within the defect. These Z dimensions can be recordedin real time with conventional dial gauge indicators, or with digitalrecording devices, or by using marking techniques. Although numerouspoints may be taken, ideally a minimum number of points are taken toaccurately define the target articular surface.

Locating surfaces or features created on the screw, (or alternatively,on the radius cover, as described in alternative embodiments herein),correlate to some surface or feature on the measuring tool and allow themeasurement of the rotational position of the points about the axis withrespect to the locating surfaces. Data recorded during the mappingprocedure can then be entered into parametric engineering designsoftware or similar algorithm to define a three dimensional surfacematched to the bearing surface geometry to be implanted and reproducethe anatomic contours mapped.

An alternative measuring device for obtaining the articular surfacedimension includes an outer marking element and an inner recordingelement. The marking element includes a sharp indenting mechanism whichwhen pressed by the surgeon creates a depression or mark in therelatively soft surface of the recording element, which deforms at thesemarked points so that they can be utilized as patient data. Therecording element also includes a surface that corresponds to thesurface of the proximal extension of the fixation screw. During themapping procedure, data points are established of the rotationalposition of the mapped articular surface relative to the screw. Thesedata points are translated to the implant geometry so that the accuraterotational location of the implant relative to the screw is maintained.

In order to secure the implant to the fixation screw, a precision taper(or other component of a mating feature) is machined into a protrusion(or other component of a mating feature) on the back of the device. Theimplant may be constructed of cobalt chromium, or other materials. Theimplant may also include a slight outward taper or protrusion along thediametrical surface to enhance load bearing or load transfer propertiesof the implant to surrounding bone. Additionally, a series of radialcuts may create surfaces that increase resistance of the implant torotational forces. These features may be located around the outerdiameter of the implant.

In another aspect, the invention includes a compass instrument formeasurement and surface preparation of the implant target sitesubsequent sizing of the implant. This compass instrument is configuredso that it can be delivered to the site arthroscopically, and whencoupled to the axis defined by the guide pin it can be used formeasuring and cutting operations.

In another embodiment, the compass instrument consists of a handle, acannulated shaft that extends through the handle, and a cannulateddistal offset arm configured to serve as a linearly adjustable mountingtool for a series of cutting blades, boring blades, or measuring probes.

With the guide pin advanced through the instrument shaft, when fittedwith a blade, a fixed length from the rotational or reference axis tothe cutting blade's cutting surface is established. This defines theradius that is effected as the instrument is rotated around the guidepin, and corresponds to the overall diameter of the implant. This sharpcutting blade is used to circumscribe and cleanly cut the surroundingarticular cartilage.

In another aspect, the invention features a bone cutting or scoringinstrument whereby the bone-cutting instrument is positioned on theguide pin reference axis and is used to prepare the target site to matchin configuration and dimension the contacting surface of the implant.The matching fit between the bone surfaces of the prepared target siteand the bone contacting surfaces of the implant can advantageouslyensure long term clinical results with the implant, as poor quality offit between bone surfaces and bone contacting surfaces of traditionalorthopedic prosthetic devices has been noted to contribute to earlyclinical failures.

Following fabrication of the implant, a second surgical procedure isperformed. The radiused cover is removed exposing a precision taper (or,alternatively, the cover may be removed during the first procedure). Apin with a distally mounted element is placed through the central lumenof the fixation screw so that the distally mounted element is securedinto the screw. This element carries one or more suture strands that nowtrail from the fixation screw. The sutures are then threaded through theimplant and a knot or bead may be created proximal to the implant. Bycontinuing to manipulate and tension the suture strands, the implant canbe brought coaxial to the fixation screw. Once coaxial, the implant isaligned via engagement of the keyed elements and driven into place witha plastic driving rod and mallet. Finally, through the guide aperture onthe surface of the implant, bone cement may be injected to enhance thecontact surface between the implant and the subchondral bone.

In another aspect, the invention further features a driver whereby theimplant is connected to the driver via a holder and a tether element,such as a suture or wire. The implant and the driver are then insertedarthroscopically. Tension is then applied to the tether element so thatthe implant is drawn back and seated on the driver. The implant can thenbe controllably delivered to the prepared target site. The seat portionof the driver may comprise a material that may be impacted to seat theimplant without damaging the implant surface.

In one aspect, a guide device for locating a guide pin or wiresubstantially normal with respect to an articular surface of bonecomprises a cannulated shaft having a distal end and a centrallongitudinal axis; and a ring portion coupled to the distal end of theshaft, the ring portion comprising a planar distal contact surfacecomprising a plurality of points radially extending from any given pointalong the central longitudinal axis of the shaft.

In another aspect, a guide device for locating a guide pin or wiresubstantially normal with respect to an articular surface of bone havingan anterior-posterior (AP) curve and a medial-lateral (ML) curvecomprises a cannulated outer shaft and a cannulated inner shaft. Theouter shaft has a central longitudinal axis and an outer component atits distal end, the outer component comprising a set of arms, and thecannulated inner shaft is slidably disposed within the cannula of theouter shaft, the inner shaft having an inner component at its distal endand sharing the central longitudinal axis of the outer shaft, the innercomponent comprising a set of arms.

In method form, a method for replacing a portion of an articular surfaceof bone comprises defining an axis generally normal to the portion of anarticular surface of bone to be replaced; excising at least the portionto be replaced by cutting the articular surface radially symmetricallyabout the axis, thereby creating an excised portion of the articularsurface; selecting an implant corresponding to the dimensions of theexcised portion from a set of variously-sized implants; and installingthe selected implant into the excised portion.

In method form, a method for replacing a portion of an articular surfaceof bone having an anterior-posterior (AP) curve and a medial-lateral(ML) curve comprises defining an axis generally normal to the portion ofan articular surface of bone to be replaced using an anterior-posterior(AP) curve and a medial-lateral (ML) curve of the articular surface;excising at least the portion to be replaced by cutting the articularsurface radially symmetrically about the axis, thereby creating anexcised portion of the articular surface; selecting an implantcorresponding to the dimensions of the excised portion from a set ofvariously-sized implants; and installing the selected implant into theexcised portion.

In a further aspect, a tool for holding an implant comprises anactivatable suction source; and an elastomeric suction tip adapted toreceive an implant, the tip being coupled to the suction source.

In method form, a method for holding an implant comprises coupling asuction source to an implant; and activating the suction source.

In method form, a method for delivering an implant comprises coupling asuction source to an implant; activating the suction source;approximating the implant to its delivery site; and applying a force tothe implant in the direction of the delivery site.

In yet another aspect, a tool for removing an implant from its deliverysite comprises a cylindrical structure having a distal end; the distalend comprising a longitudinal central axis, a circular blade portionhaving a leading edge comprising a blade surface turned on thedistal-most portion, and a lip portion disposed proximally with respectto the leading edge; and a plurality of slits parallel to thelongitudinal central axis of the distal end formed along the length ofthe cylindrical structure, so as to permit sufficient outward expansionof the distal end to accommodate the top edge of an implant therein.

In method form, a method for removing an implant from its delivery sitecomprises disposing the lip portion of the leading edge of the distalend of a removal tool over the upper edge of an implant seated in itsdelivery site; and applying a pulling force to the removal tool.

In still another aspect, a device for mapping a portion of an articularsurface of bone comprises a handpiece, an inner shaft, a contact tip, arotary measuring element, and a linear measuring element. The innershaft runs along the length of and is disposed within the handpiece andcomprises a mating feature for mating with a fixed element locatedsubstantially normal with respect to an articular surface. The contacttip is slidably and rotatably disposed about the inner shaft. The rotarymeasuring element is coupled to and rotating with the contact tip. Thelinear measuring element is nested concentrically and coaxially to therotary measuring element, and coupled to and moving linearly with thecontact tip.

A generic bone implant, or set of standardized implants, may further becreated based on using a guide device to develop an axis normal to anarticular surface of bone and collecting only one or two data points. Ageneric cutting tool may be used to cut the bone to a point where ageneric implant can be used. Several improved tools relating to theprocedure for using such an implant, as well as methods for usingimplants consistent with the invention are further describedhereinbelow, including: single-axis and biaxial drill guide tools andmethods, generic single-axis implant methods and devices, genericbiaxial implant methods and devices, tools and methods for holding ordelivering an implant, removal or revision tools and methods, digitalmeasuring systems and methods, and set of measuring gauges fordetermining the appropriate implant dimensions.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary side view of a knee having therein an exemplaryassembled fixation device and implant of the joint surface repair systemsurgically implanted by the method in one embodiment of the presentinvention;

FIG. 2a is an exploded side view of an exemplary fixation screw andhex-shaped proximal extension in one embodiment of the presentinvention;

FIG. 2b is an exploded perspective view of an exemplary fixation screwand hex-shaped proximal extension in one embodiment of the presentinvention;

FIG. 3a is a side view of an exemplary assembled fixation screw and hexshaped extension in one embodiment of the present invention;

FIG. 3b is an exploded perspective view of another exemplary fixationscrew and implant in one embodiment of the present invention;

FIG. 4a is a perspective view of the upper surface of an exemplaryimplant in one embodiment of the present invention;

FIG. 4b is a side view of an exemplary implant in one embodiment of thepresent invention;

FIG. 4c is a perspective view of the lower surface of an exemplaryimplant in one embodiment of the present invention;

FIG. 5a is a side view of an exemplary assembled fixation device andimplant in one embodiment of the present invention;

FIG. 5b is a perspective view of an assembled fixation device andimplant in one embodiment of the present invention;

FIG. 5c is a perspective view of the upper surface of an exemplaryimplant, in one embodiment of the present invention;

FIG. 5d is a perspective view of the lower surface of an exemplaryimplant, in one embodiment of the present invention;

FIG. 6a is a sectional view of a knee having damaged articularcartilage, showing an exemplary guide pin drilled into the centralportion of the defect and an arthroscope being disposed adjacentthereto, in a surgical procedure consistent with one embodiment of thepresent invention;

FIG. 6b is a side view of the distal tip of an exemplary drill devicefor boring a pilot hole to receive an exemplary fixation screw, in oneembodiment of the present invention;

FIG. 7a is a sectional view of a knee having damaged articularcartilage, showing an exemplary fixation screw being driven into thedefect by an exemplary socket type driver arranged on the guide pin, ina surgical procedure consistent with one embodiment of the presentinvention;

FIG. 7b is a side view of the exemplary fixation screw, socket typedriver and guide pin of FIG. 7a , illustrating the hex shaped proximalextension in a cross-sectional view, in a surgical procedure consistentwith one embodiment of the present invention;

FIG. 8a is a perspective view of a knee having damaged articularcartilage, showing an exemplary fixation screw and hex-shaped proximalextension implanted in the defect after removal of an exemplary sockettype driver and guide pin, in a surgical procedure consistent with oneembodiment of the present invention;

FIG. 8b is a sagital view of the exemplary fixation screw and hex-shapedproximal extension of FIG. 8a implanted in the defect after removal ofan exemplary socket type driver and guide pin, in a surgical procedureconsistent with one embodiment of the present invention;

FIG. 8c is a perspective view of an exemplary fixation screw, proximalextension and cover, in one embodiment of the present invention;

FIG. 9a is a sectional view of an exemplary fixation screw andhex-shaped proximal extension implanted in the defect with the exemplaryguide pin replaced and an exemplary measuring tool arranged thereon, ina surgical procedure consistent with one embodiment of the presentinvention;

FIG. 9b is a side partial cross-sectional view of the exemplary fixationscrew and hex-shaped proximal extension of FIG. 9a implanted in thedefect with the exemplary guide pin replaced and an exemplary measuringtool arranged thereon, in a surgical procedure consistent with oneembodiment of the present invention;

FIG. 9c is a perspective view of an exemplary fixation screw andproximal extension, with the cover removed, in one embodiment of thepresent invention;

FIG. 10a is a sectional view of an exemplary fixation screw andhex-shaped proximal extension implanted in the defect, after removal ofthe hex-shaped proximal extension, with an exemplary pin and suturestrands placed therethrough, in a surgical procedure consistent with oneembodiment of the present invention;

FIG. 10b is a side partial cross-sectional view of the exemplaryfixation screw and hex-shaped proximal extension of FIG. 10a , implantedin the defect, with an exemplary pin and suture strands placedtherethrough, in a surgical procedure consistent with one embodiment ofthe present invention;

FIG. 11a is a sectional view of an exemplary fixation screw implanted inthe defect, with an exemplary pin and suture strands placedtherethrough, showing the implanted fixation screw with the implantbeing tensioned on the suture strands, in a surgical procedureconsistent with one embodiment of the present invention;

FIG. 11b is a partial cross-sectional view of the exemplary fixationscrew of FIG. 9a implanted in the defect, showing the implant positionedin the interchondular notch, in a surgical procedure consistent with oneembodiment of the present invention;

FIG. 12 is a sectional view of an exemplary fixation screw implanted inthe defect, wherein, after placement of the implant and removal of thesuture strands, the implant is driven into place with an impactor andhammer, in a surgical procedure consistent with one embodiment of thepresent invention;

FIG. 13 is a side cross-sectional view of an exemplary fixation screwimplanted in the defect, after placement of the implant, wherein, afterremoval of the impactor and hammer, cement is injected between theimplant and the bone, in a surgical procedure consistent with oneembodiment of the present invention;

FIG. 14a is a schematic representation of the two datum curves used todefine a patient-specific three-dimensional surface for construction ofthe articular or lower surface of an implant in one embodiment of thepresent invention;

FIG. 14b is a top view of an exemplary hex-shaped proximal extension inone embodiment of the present invention;

FIG. 14c is a perspective view of the bone-contacting or upper surfaceof an exemplary implant, in one embodiment of the present invention;

FIG. 15a is a perspective view of an exemplary compass instrument, inone embodiment of the present invention;

FIG. 15b is a perspective view of the distal offset arm of an exemplarycompass instrument and cutting blade to be mounted thereon, in oneembodiment of the present invention;

FIG. 15c is a perspective view of an exemplary driver, showing anexemplary implant on an exemplary tether element, in one embodiment ofthe present invention;

FIG. 15d is a perspective view of an exemplary driver, showing anexemplary implant tensioned on an exemplary tether element, in oneembodiment of the present invention;

FIG. 16 is a perspective view of an exemplary compass instrument andcutting blade mounted on an exemplary guide pin, in one embodiment ofthe present invention;

FIG. 17a is a perspective view of another exemplary cutting blade, inone embodiment of the present invention;

FIG. 17b is a perspective view of an exemplary measuring probe, in oneembodiment of the present invention;

FIG. 17c is a perspective view of an exemplary multi-faced blade mountedin the distal offset arm of an exemplary compass instrument, in oneembodiment of the present invention;

FIG. 18a is a perspective view of an exemplary site preparation andcutting device, in one embodiment of the present invention;

FIG. 18b is a cross sectional view of the exemplary site preparation andcutting device of FIG. 18a , in one embodiment of the present invention;

FIG. 18c is a perspective view of another exemplary site preparation andcutting device, in one embodiment of the present invention;

FIG. 18d is a side view of another exemplary site preparation andcutting device, in one embodiment of the present invention;

FIG. 18e is a perspective view of another exemplary site preparation andcutting device, in one embodiment of the present invention;

FIG. 19a is a sectional view of the upper surface of an exemplaryimplant, in one embodiment of the present invention;

FIG. 19b is a side view of a portion of the exemplary implant of FIG.19a , in one embodiment of the present invention;

FIG. 19c is a perspective view of the upper surface of the exemplaryimplant of FIG. 19a , in one embodiment of the present invention;

FIG. 19d is an exploded perspective view of another exemplary implantwith taper lock ring, washer and suture, in one embodiment of thepresent invention;

FIG. 19e is a top perspective view of the exemplary implant of FIG. 19dseated in the taper lock ring, in one embodiment of the presentinvention;

FIG. 19f is a bottom perspective view of the exemplary implant of FIG.19d seated in the taper lock ring, with washer and suture, disposedwithin an incision near the defect site, in one embodiment of thepresent invention;

FIG. 19g is a perspective view of the exemplary implant of FIG. 19dseated in the taper lock ring, with washer and suture, wherein thesuture is threaded through an aperture at the distal end of a seatingtool, at a first point in time during the process of seating the implantinto the defect site, in one embodiment of the present invention;

FIG. 19h is another perspective view of the exemplary implant of FIG.19d seated in the taper lock ring, with washer and suture, wherein thesuture is threaded through an aperture at the distal end of a seatingtool, at a second point in time during the process of seating theimplant into the defect site, in one embodiment of the presentinvention;

FIG. 19i is another perspective view of the exemplary implant of FIG.19d seated in the taper lock ring, wherein the distal end of a seatingtool is disposed onto the implant, at a third point in time during theprocess of seating the implant into the defect site, in one embodimentof the present invention;

FIG. 20a is a perspective view of an exemplary inner recording elementof an exemplary measuring device, in one embodiment of the presentinvention;

FIG. 20b is a perspective view of an exemplary outer marking element ofan exemplary measuring device, in one embodiment of the presentinvention;

FIG. 20c is a cross-sectional perspective view of an exemplary measuringdevice showing an exemplary inner recording element and an exemplaryouter marking element, in one embodiment of the present invention;

FIG. 20d is an exploded perspective view of another exemplary measuringdevice, in one embodiment of the present invention;

FIG. 20e is a perspective view of the exemplary measuring device of FIG.20d , illustrating an exemplary scroll alignment feature, in oneembodiment of the present invention;

FIGS. 20f and 20g are side views of the exemplary measuring device ofFIG. 20d illustrating the translational motion of the handle withrespect to the tip of the device, in one embodiment of the presentinvention;

FIG. 20h is a perspective view of the distal end of the exemplarymeasuring device of FIG. 20d , in one embodiment of the presentinvention;

FIG. 20i is a perspective view of the distal end of the exemplarymeasuring device of FIG. 20d with outer element, disposed upon the innerelement engaging a mating feature of the screw, in one embodiment of thepresent invention;

FIG. 21 is a perspective view of an exemplary unitary implant, in oneembodiment of the present invention;

FIG. 22 is a perspective view of a defect site with a keyed aperture forreceiving the exemplary unitary implant of FIG. 21, in one embodiment ofthe present invention;

FIG. 23 is a perspective view of an exemplary composite implant, in oneembodiment of the present invention;

FIG. 24 is a perspective view of another exemplary composite implant, inone embodiment of the present invention;

FIG. 25 is a perspective view of an exemplary implant illustrating thegeometry of said implant for use in an algorithm for establishingminimum implant thickness, in one embodiment of the invention;

FIG. 26 is a perspective view of an exemplary implant illustrating thegeometry of said implant for use in an algorithm for establishingminimum implant thickness, in one embodiment of the invention;

FIG. 27a is a perspective view of an exemplary drill guide device in anexemplary generic bone implant embodiment of the present invention;

FIG. 27b is a perspective view of another exemplary drill guide devicein an exemplary generic bone implant embodiment of the presentinvention;

FIG. 28a is a top sectional view of the anterior-posterior plane of anarticulating surface in an exemplary generic bone implant embodiment ofthe present invention;

FIG. 28b is a side sectional view of the medial-lateral plane of anarticulating surface in an exemplary generic bone implant embodiment ofthe present invention;

FIG. 29 is a perspective view of the use of an exemplary drill guide inan exemplary generic bone implant embodiment of the present invention,as the drill guide is brought up to a lesion site of the articulatingsurface;

FIG. 30 is a perspective view of the use of an exemplary drill guide inan exemplary generic bone implant embodiment of the present invention,as the drill guide is seated into position and a guide pin is driventhrough the drill guide;

FIG. 31 is a perspective view of the articulating surface in anexemplary generic bone implant embodiment of the present invention, as abone drill is passed over the guide pin to create a pilot hole for thescrew;

FIG. 32 is a cross-sectional view of the articulating surface in anexemplary generic bone implant embodiment of the present invention, asthe screw is driven into the pilot hole with a cap positioned into thescrew;

FIG. 33 is a cross-sectional view of the articulating surface in anexemplary generic bone implant embodiment of the present invention, asthe cap is removed and a rod is inserted into the screw, and the guideis positioned back over the rod and returned to its position in contactwith the articular surface;

FIG. 34 is a side perspective view of the articulating surface in anexemplary generic bone implant embodiment of the present invention, asthe guide is used to take a depth measurement needed for implantgeometry;

FIG. 35 is a top perspective view of the lower surface of an exemplaryimplant in an exemplary generic bone implant embodiment of the presentinvention;

FIG. 36 is a side perspective view of an exemplary implant in anexemplary generic bone implant embodiment of the present invention;

FIG. 37 is a side perspective view of another exemplary implant in anexemplary generic bone implant embodiment of the present invention;

FIG. 38 is a perspective view of the articulating surface in anexemplary generic bone implant embodiment of the present invention, asthe implant site is reamed with a cutting/reaming tool in preparationfor receiving an implant;

FIG. 39 is a top perspective view of an alternative exemplarycutting/reaming tool in an exemplary generic bone implant embodiment ofthe present invention,

FIG. 40 is a side perspective view of an exemplary cleaning tool forcleaning the female taper of the screw prior to delivery of the implant,in an exemplary generic bone implant embodiment of the presentinvention;

FIG. 41 is a side perspective view of an exemplary suction tool forholding and delivering the implant, in an exemplary generic bone implantembodiment of the present invention;

FIG. 42 is a side perspective view of an exemplary suction tool holdingan implant in place, in an exemplary generic bone implant embodiment ofthe present invention;

FIG. 43 is a side cross-sectional view of an exemplary suction toolholding an implant in place, with an implant in place, in an exemplarygeneric bone implant embodiment of the present invention;

FIG. 44 is a top perspective view of the articulating surface in anexemplary generic bone implant embodiment of the present invention, withthe implant driven into its final position;

FIG. 45 is a side perspective view of an exemplary removal/revision toolin an exemplary generic bone implant embodiment of the presentinvention;

FIG. 46 is a side perspective view of an exemplary removal/revisiontool, with an implant in place, in an exemplary generic bone implantembodiment of the present invention;

FIG. 47 illustrates an exemplary alternatively-keyed embodiment of thescrew and the exemplary alternatively-keyed implant to which it isadapted to mate, in an exemplary embodiment of the present invention;

FIG. 48 illustrates a side cross-sectional view of an exemplaryalternatively-keyed embodiment of the screw, in an exemplary embodimentof the present invention;

FIG. 49 illustrates a side perspective view of the articular surface ofa lesion site and an exemplary biaxial measuring tool for developing anaxis normal to the articular surface, in one embodiment of the presentinvention

FIG. 50 illustrates another side perspective view of the articularsurface of a lesion site and an exemplary biaxial measuring tool fordeveloping an axis normal to the articular surface, in one embodiment ofthe present invention;

FIG. 51 illustrates a side exploded view of an exemplary biaxialmeasuring tool, in one embodiment of the present invention;

FIG. 52 illustrates a top perspective view of the distal end of anexemplary biaxial measuring tool in a first position, in one embodimentof the present invention;

FIG. 53 illustrates a top perspective view of the distal end of anexemplary biaxial measuring tool in a second position, in one embodimentof the present invention;

FIG. 54 illustrates an exemplary digital measuring system in oneembodiment of the present invention;

FIG. 55 illustrates an exploded perspective view of an exemplaryhandpiece in an exemplary digital measuring system in one embodiment ofthe present invention;

FIG. 55a illustrates a top perspective cutaway view of an exemplaryprinted linear index strip passing through an exemplary linear head forreading, in an exemplary handpiece in an exemplary digital measuringsystem in one embodiment of the present invention;

FIG. 55b illustrates a top perspective cutaway view of an exemplaryprinted rotary index strip passing through an exemplary rotary head forreading, in an exemplary handpiece in an exemplary digital measuringsystem in one embodiment of the present invention;

FIG. 55c illustrates an exemplary linear index strip in an exemplaryhandpiece in an exemplary digital measuring system in one embodiment ofthe present invention;

FIG. 55d illustrates an exemplary rotary index strip in an exemplaryhandpiece in an exemplary digital measuring system in one embodiment ofthe present invention;

FIG. 56a illustrates a side perspective view of an exemplary handpiecewith the probe assembly removed, in an exemplary digital measuringsystem in one embodiment of the present invention;

FIG. 56b illustrates a side perspective view of an exemplary handpiece,including the probe assembly, in an exemplary digital measuring systemin one embodiment of the present invention;

FIG. 57 illustrates a top perspective view of an assembled exemplaryhandpiece, in an exemplary digital measuring system in one embodiment ofthe present invention;

FIG. 58 illustrates a side perspective view of an assembled exemplaryhandpiece, in an exemplary digital measuring system in one embodiment ofthe present invention;

FIG. 59 illustrates a top cross-sectional view of an assembled exemplaryhandpiece, in an exemplary digital measuring system in one embodiment ofthe present invention;

FIG. 60 illustrates a side cross-sectional view of an assembledexemplary handpiece, in an exemplary digital measuring system in oneembodiment of the present invention; and

FIG. 61 illustrates a side cutaway perspective view of an exemplary baseunit, in an exemplary digital measuring system in one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As an overview, FIG. 1 shows a surgically implanted articular jointsurface repair system consistent with the present invention. As shown,the assembled fixation device includes fixation screw 10, implant 40,and anchoring pin 5, implanted in the defect in the medial femoralchondral surface 55 of knee 50. Implant 40 is configured so that bearingor bottom surface 41 of the implant reproduces the anatomic contours ofthe surrounding articular surface of the knee 50.

As illustrated in FIGS. 2a, 2b and 3a , fixation screw 10 comprisesthreads 12 running the length of the screw from tapered distal tip 11 tohex-shaped drive 15. In the embodiment shown, the screw includes atapered distal end 11, and aggressive distal threads 12, so that, asscrew 10 is driven into the subchondral bone 100 (as shown in FIG. 7a )the screw dilates open and radially compress the subchondral bone,increasing its local density and thereby increasing the fixationstrength of the screw. The screw 10 may taper down to the distal end 11,and the diameter of the screw may become greater and more uniform at thecenter thereof, so that adjustment of the depth of the screw 10 withrespect to the subchondral bone 100 does not significantly furtherincrease or decrease the compression of the subchondral bone.

One or more milled slots 13 run the length of the uniform diameterportion of the screw 10. Slots 13 ensure that as healing or tissuein-growth begins, migrational or rotational movement of the screw isinhibited. The screw 10 is configured to be driven by a female or sockettype driver 2 as shown in FIG. 7b , which engages a hex-shaped drive 15located toward the proximal end 17 of the screw. A cylindrical proximalextension 14 (which may, alternatively, be a recess 303 which mates witha plug or other protrusion on the implant surface, as shown in FIG. 8c )extends from hex-shaped drive 15, which eventually serves as a fixationelement for surface prosthetic implant 40. Through hole 16 runs throughthe central axis of the screw. Hex-shaped cover 30 (which may,alternatively, be a plug 301, for mating with a fixation element 302having a recess, as shown, e.g., in FIGS. 3b, 8c, and 9c , and describedin the following paragraph) is configured to engage the cylindricalproximal extension 14 of the screw 10 to prevent exposure of thecylindrical extension from inadvertent contact or damage. The hex-shapedcover 30 is finished with a radiused proximal end 31 that assists in thevisual determination of the correct depth setting of the screw. Throughhole 32 in the hex-shaped cover 30 corresponds with through hole 16 inthe fixation screw 10.

Alternatively, as shown in FIGS. 3b, 8c, and 9c , the female-shapedcover may instead be a plug 301 having a male-shaped mating component305, for mating with a fixation element 302 of a screw 10′ having arecess 303. Additionally, the shape of the cover and plug, or otherrecessed, protruding, or mating components may be other than hexagonal,and those in the art will recognize that one of any number of shapes orconfigurations for such components may be employed in a device or methodconsistent with the invention.

Also, while many of the components described herein are cannulated,having guide apertures, through holes, and/or central lumina along theirlength, for disposing such components about a guide rod for properlocation of the components with respect to the articular surface, itshould be recognized that a suture 313 or other flexible element, orother guide feature may be used in place of a guide rod, or a guide rodor wire may be eliminated altogether from one or more steps consistentwith the invention described herein. As shown in FIG. 8c , the suture313 may be fixedly or removably attached to the plug 301.

As shown in FIGS. 4a, 4b and 4c , implant 40 comprises lower bearingsurface 41, top surface 42 and protrusion 45 located centrally on thebottom surface. As the top surface 42 of the implant 40 is not a bearingsurface, and instead is fixed into subchondral bone 100, a series ofstepped machine cuts 43 following the contours of the defect arecreated. By creating stepped machine cuts 43 a contoured contact surfacematching the defect in the subchondral bone 100 is created. This contactsurface results in an increased surface area that should enhanceresistance to loosening of the implant 40 via rotational ortranslational loading. In the illustrated embodiment, the stepped cutsare shown as square cross-section cuts, but the cuts may be circular,triangular, or another configuration.

In order to secure the implant 40 to the fixation screw 10, precisiontaper 44 is machined into or onto a protrusion 45 on the top surface 42of the implant. The precision taper 44 is configured to engage thecylindrical proximal extension 14 of the screw 10, once the hex-shapedcover 30 has been removed therefrom. Taper 44 may be mated withextension 14 so that a friction fit is provided between these surfaces.The assembled fixation device is shown in FIGS. 5a and 5b .Alternatively, other engagement mechanisms such as snap-fits,press-fits, threads, or coupling elements, for example, may also beused. In one embodiment, leading pin 47 arranged on the protrusion 45assists penetration into subchondral bone. Also, in one embodiment,guide aperture 46 passes through the top 42 and bottom 41 surfaces ofthe implant 40, just slightly off center of the reference axis 20A.Alternatively, guide aperture 46 may be located in the center of theimplant 40 and corresponds to through hole 16 running through thecentral lumen in the fixation screw 10. Bone cement may be injectedthrough guide aperture 46 on the surface of the implant 40 and throughhole 16 in the fixation screw 10, to enhance the contact surface betweenthe device and the subchondral bone. In one embodiment, the implant isconstructed of cobalt chromium, although other materials may be used,including implantable plastics. Additionally, biologically activecoatings or surface treatments (e.g., to enhance bone ingrowth orimprove wear properties) may be utilized or combined as laminates,particularly with respect to the bearing surfaces and bone contactingsurfaces. Further exemplary materials that may be used in fabricating animplant consistent with the invention are described hereinbelow.

As shown in FIG. 3b , it is noted that precision taper 44 may be amale-shaped component 304 instead of the above-described femalecomponent 44. In this configuration, the male-shaped component 304 ofthe implant 40′ is configured for mating with a fixation element 302 ofthe screw 10′ having a recess 303 adapted to receive the male-shapedcomponent 304.

By way of example, FIGS. 6a -13 depict one exemplary joint surfacemethodology of the present invention. FIG. 6a shows a focal defect 1 ofthe articular surface 55 of the femoral chondyle bone of the knee 50.This defect is identified by arthroscope 25 inserted in the area of thedefect 1 during a diagnostic arthroscopy or surgical arthroscopy. Thedisclosed surgical intervention begins by drilling a guide pin 20defining reference axis 20A into the central portion of the defect 1 viaan incision 200 typical of arthroscopic procedures. Placement of thispin may be done using visual, freehand techniques, or may be locatedcentrally by using outer element 71 of a measuring tool 70 (as shown inFIGS. 9a and 9b ), or other aiming device or technique, to define acenter. This reference axis 20A serves to establish a working axislocated central to the defect 1 for the procedures that follow, andarthroscope 25 may be used to view the joint for purposes ofestablishing a reference axis 20A generally perpendicular to andbisecting the existing articular surface 55 defined by radii 60 and 61,as shown in FIG. 8b . Referring to FIGS. 7a, 7b, 8a and 8b , fixationscrew 10 and hex-shaped cover 30 are driven into the defect 1 in thesubchondral bone 100 by socket-type driver 2 mounted over (i.e., about)guide pin 20 located on reference axis 20A. Under arthroscopic view, thedepth of fixation screw 10 may be adjusted by driver 2 so that thebottom of the radiused surface 31 of the hex-shaped cover 30 ispositioned tangent to the radii 60 and 61 that define the existingarticular surface 55. The guide pin 20 is removed and the knee 50 isarticulated through its range of motion to ensure that the height of theradiused surface 31 of the hex-shaped cover 30 is proper, since theprosthetic surface 41 of the implant 40 is created also to be tangent tothis radiused surface 31. The depth positioning of the radiused surface31 of the hex-shaped cover 30 establishes a point of origin or areference point for all future measuring and machining operations.Arthroscopic examination may be carried out from multiple arthroscopicviews to confirm positioning.

A drill mechanism 306, as illustrated in FIG. 6b , may be used to bore apilot hole for receiving a fixation screw 10 (as shown, e.g., in FIGS.2a, 2b and 3a ). As shown, the drill may have a shank portion 307 and abit portion 308. The bit portion 308 may include a spiral or parabolicfluted tip 309 having proximal 310, medial 311, and distal 312 portions.The root diameter at the medial portion 311 is substantially equal tothe diameter of the fixation screw 10, and the diameter decreases as thedistal portion 312 tapers away from the shank 307. The proximal portion310 of the bit 308 may be used as a visual indicator during drilling, todetermine the point at which the proper bore depth has been attained.The drill mechanism may have a central lumen (not shown) having adiameter slightly greater than the diameter of the guide pin 20 (asillustrated in FIG. 6a ) running along its length, so that, with theguide pin 20 in place, the drill 306 may be disposed about the guide pin20 during drilling to ensure proper location of the pilot hole withrespect to the articular surface 55. Alternatively, a self-drilling orself-tapping screw, may be used, as those skilled in the art willrecognize.

For surface preparation and accurate measurement of the implant site andthe subsequent sizing of the implant, instrument 120 is provided. Thecompass instrument 120 may be configured to serve as a mounting tool fora number of functional blades or tips and when located about the axis20A, via guide rod 20, may be used for measuring and cutting operations.In the embodiment shown in FIG. 15a , compass instrument 120 includeshandle 110, a cannulated shaft 111 that extends through the handle, anda cannulated distal offset arm 112. The instrument may be rigid inconstruction and may be a durable reusable and resterilizableinstrument. The distal offset arm 112 is configured so that it can beintroduced into a site through an incision 200 typical of anarthroscopic procedure. Once the distal offset arm 112 has fullypenetrated the incision and enters the site, shaft 111 can be angularlyrepositioned so that it becomes more coaxial to the reference axis 20Aand advanced in-line with the reference axis 20A towards the implanttarget site. While performing this maneuver to position the compassinstrument 120, the guide pin 20 should be removed from its position inthe defect 1. When compass 120 is in its proper position at or near theimplant target site, the guide pin 20 is delivered through theinstrument cannulation 113, re-establishing the working (reference) axis20A used to define the implant geometry.

Referring to FIG. 15b , within offset arm 112 is a slotted surface 114for engaging a series of cutting blades 121, boring blades 124, ormeasuring probes 122. The slots 115 are configured so that said seriesof cutting blades 121, boring blades 124 (FIG. 17c ), measuring probes122, 123 (FIGS. 17a, 17b ), or like elements may be partiallyconstrained or fixed in position such that they may be adjusted linearlyalong the length of the slotted surface 114 over a defined distance oftravel. Intersecting the plane of travel defined by slotted surface 114and slots 115, is the cannulation 113.

As illustrated in FIG. 16, when fitted with a cutting blade 121, andwith the guide pin 20 advanced through the shaft 113 of instrument 120,so that the guide pin passes through a closely sized hole 116 in thecutting blade, the blade's position becomes fully constrained. Whenconstrained in this fashion, a fixed length from the rotational orreference axis 20A to the cutting surface 117 of cutting blade 121 isestablished. This defines the radius that is effected as the instrument120 is rotated around the guide pin 20, and corresponds to the overalldiameter of the implant 40 that is delivered to the fully prepared site.The cutting blade 121 is used to circumscribe and cleanly cut thesurrounding articular cartilage.

In an alternative embodiment, as shown in FIGS., 17 a and 17 b, blade123 and measuring probe 122, respectively, may have multiple holes 118that defines that probe/blade's functional diameter. In addition, theblades may be specifically configured so that staged or sequential cutsof varying depths and diameters can be performed within the procedure.Also, such a blade can be configured by providing a readable scale 119corresponding to the hole 118 pattern, so that the surgeon may determineand set the appropriate diameter as needed by positioning the guide pin20 in the corresponding hole. As the readable scale 119 may be locatedon the blade 123 with respect to the blade's cutting surface 117, a highdegree of positional accuracy may be achieved as the scale may bedefined specifically for each type of blade. This approach creates aninexpensive means of providing sharp blades of varying diameters andvarying blade types without a large inventory of size- and type-specificblades. Referring to FIG. 17b , rounded tip 109 of measuring probe 122can be used to determine the appropriate diameter and can be similarlysized and secured in the compass instrument 120. The tip 109 may berounded to prevent marring of the articular surface. FIG. 17c shows aboring bit or bone cutting blade 124 with multiple cutting surfaces 107and 108 configured in this fashion.

Turning now to FIGS. 9a and 9b , with the guide pin 20 replaced, ameasuring tool 70 is inserted so that the reference axis 20A isutilized. A central element of the measuring tool 70 is a post 75 thatis static, establishes the axial location of the point of origin 80, andmates with a rotational location feature within the screw 14. Byrotating the outer arm or outrigger 71 of the measuring tool 70 relativeto the static post 75 while also maintaining contact with the articularsurface 55, an axial displacement or Z dimension can be establishedrelative to the point of origin 80 for any point along the sweep of theoutrigger. Each such Z dimension may be recorded in real time withconventional dial gauge indicators 72 or with a digital recordingdevice, such as disclosed in U.S. Pat. No. 5,771,310 to Vannah, or byusing other known marking techniques. Although numerous points may betaken, ideally a minimum number of points are taken to define accuratelythe target articular surface. In other embodiments, multiple outriggersthat embody different diameters or an adjustable outrigger may be usedto map larger defects, and also to determine the final diameter of theprosthetic surface that fits within the defect. It is noted that themeasuring tool may comprise a spring or other tensioning device (notshown), for urging the outrigger distally with respect to the handle ofthe tool. In this aspect, the outrigger is manually pressed against thearticular cartilage, so as to maximally compress the articular cartilageupon recording data points, so that the data points taken are of amaximally “loaded” or “compressed” dimension.

FIGS. 20a, 20b and 20c show an alternative measuring and mapping device210 for obtaining the articular surface dimension, comprising housing217 and a recording element 218. As shown in FIG. 20a , recordingelement 218 includes upper portion 219, flange 222 and calibrated lowerportion 220. Key-shaped surface 221 located at distal end 225 ofrecording element 218 is configured to engage a reciprocal key-shapedsurface in the proximal extension 14 of fixation screw 10, or, forexample, a key shaped cover arranged on the proximal end of the screw(not shown). The upper portion 219 of recording element 218 may beconstructed of a relatively soft or other deformable material that canbe marked with patient data. Cannulated shaft 223 runs through thecentral lumen of the recording element 218. As shown in FIG. 20b ,housing 217 includes a marking mechanism 224 located on the upperportion 226 of the housing, at or within window or aperture 230. Anindexing indicator 228 is located on the lower portion 227 of thehousing 217, at window or opening 229.

Turning to FIG. 20c , recording element 218 is inserted in housing 217of measuring and mapping device 210, so that the distal end 225 ofrecording element 218 appears through opening 232. Tensioning means (notshown) in the device 210, enables recording element 218 to movelongitudinally within housing 218. With the guide pin 20 replaced, themeasuring device 210 is inserted on the guide pin on reference axis 20Aso that key-shaped surface 221 engages the corresponding keyed surfaceof the screw and is maintained in static position thereby. Thesekey-shaped surfaces establish the rotational position of the articularsurface points to be mapped relative to the screw. During the measuringand mapping procedure, the surgeon rotates housing 217 and outer arm oroutrigger 231 located at the distal end 235 of housing. By depressingmarking mechanism 224, a series of depressions or marked points 240 isestablished in the relatively soft surface of the upper portion 219 ofthe recording element 218, which deforms at these marked points so thatthey can be utilized as patient data. Indexing indicator 228 andcalibrated lower portion 220 of recording element 217 allow forcontrolled rotational movement between housing 217 and recording element218. In this way, the rotational position of the mapped articularsurface points 235 relative to the screw 10 as appreciated by outer armof outrigger 231, is translated to the implant geometry as a feature sothat the accurate rotational location of the implant 40 relative to thescrew 10 is maintained.

For example, as shown in FIGS. 8b and 9b , to accurately reproduce thetwo radii 60 and 61 that locally define the articular surface 55, fourpoints, 81 a and 81 b, and 82 a and 82 b, and the point of origin 80 arerecorded. As any three points in a single plane define a curve, byrecording points 81 a and 81 b and the point of origin 80, radius 60defining the medial-lateral aspect 68 of the chondyle can be determined.By recording points 82 a and 82 b and the point of origin 80, the radius61 defining the anterior-posterior aspect 69 of the chondyle can bedetermined. In the example provided, in order to maintain therelationship between these two defined radii, 60 and 61, the measuringtool 70 is constructed so that it can be accurately indexed from a fixedstarting point along 90 degree intervals to capture or map said fourpoints 81 a, 81 b, 82 a and 82 b, over the course of its revolution.

Locating surfaces or features created on the radius cover 30, or alongsome length of the fixation screw 10, hex-shaped drive surface of thescrew 14 or on the cylindrical proximal extension (or recess) of thescrew 14, correlate to some surface or feature on the measuring tool 70and allow the measurement of the rotational position of the fourmeasured points 81 a, 81 b, 82 and 82 b, about the reference axis 20Awith respect to said locating surfaces. This data becomes important inconfiguring the implant 40 with respect to the fixation screw 10 so thatthe proper orientation of said measured points to fabricated geometry ismaintained. Of course, such measuring tool can be configured to measureany number of points at any interval desired.

While the measurements are illustrated in FIGS. 9a and 9b as being takenfrom the bottom of the radiused surface 31 of the hex-shaped cover 30 ofthe screw, the measurements may alternatively be taken from the top ofthe screw 10′ itself, as shown in FIG. 9c . As shown, in thisembodiment, a key 315 or other alignment feature may be provided, toindicate the starting point for taking measurements. In thisconfiguration, the measuring tool used, as well as the implantmanufactured, both have a mating feature matching the key 315, forproperly locating the starting point of the measurements taken andthereby subsequently properly aligning the implant with respect to thedefect.

Other embodiments of measuring and recording tools are possible. Onesuch embodiment of a measuring and recording tool 210′ is shown in FIGS.20d-20i . As shown, measuring tool 210′ comprises a handle 316, outershaft 333, inner shaft 330, scroll 317, a tactile feedback portion 318,ring 320 having a button 321 in communication with a sharp marking point326 thereunder, a rotating portion 322 having a rotational lock 323which prevents rotation of the rotating portion 322 when engaged, and anoutrigger portion 324. The handle 316 remains fixed during rotation anddoes not move while the tool 210′ is used for measuring. Instead, therotating portion 322 is rotated to a start position and the rotationallock is engaged, securing the rotating portion 322 to the tactilefeedback portion 318 and thereby preventing its rotation. The scroll 317is configured with a notch 325 or similar mating feature to align with acorresponding mating feature (not shown) of the handle 316, such thatthe scroll can only align at one rotational point, at 0 degrees, withrespect to the handle 316 upon loading into the tool 210′, e.g., by“snapping” into place. The sharp marking point 326 located inside thering 320 under the sharp marking point 326, marks a point of depressioninto the scroll 317 while first button 321 is being depressed. Insteadof marking by making depressions on a scroll or spool, marking couldalternatively be made upon nearly any surface, e.g., using ink to recordon a paper spool, or by digital means.

As shown in FIGS. 20f and 20g , outer shaft 333, which is fixedlycoupled to rotating portion 322, outrigger 324 and ring 320, is freelyrotatably disposed about inner shaft 330 and slidably disposed aboutinner shaft 330 within a range bounded by points 334 and 337. In FIG.20f , the outrigger 324 is retracted, and outer shaft 333 is located ata position of origin along a z-axis parallel to the inner 330 and outer333 shafts, such that the proximal end of the ring 320 is located atposition 335. In FIG. 20g , the outrigger 324 is extended, and outershaft 333 is located at a position 0.250 in. (0.64 cm.) from the originof the z-axis parallel to the inner 330 and outer 333 shafts, such thatthe proximal end of the ring 320 is located at position 335′. The motionof the sliding of the outer shaft 333 about inner shaft 330 duringmarking is translated via the outer shaft 333, rotating portion 322 andring 320 (including marking button 321 and marking point 326) to alocation along the scroll 317. Thus, as the user rotates outrigger 324by rotation of rotating portion 322, the outrigger moves along thearticular surface proximally or distally with respect to the innershaft, and the displacement of the outrigger 324 along a z-axis parallelto the inner 330 and outer 333 shafts may be marked on the scroll 317 bydepression of the button 323 at various points along the rotation of theoutrigger 324. The tactile feedback portion 318 has a series ofdepressions 319 or other tactile feedback means, e.g. spring ballplungers which engage in indentations (not shown) in the inner shaft330, spaced at 90 degrees from one another, so that when the rotationallock 323 is engaged as rotating portion 322 is being rotated, the userfeels a “click” or other tactile feedback to indicate to the user therotational location of the rotating portion 322 at 90 degree intervalswith respect to the handle 316, i.e., at 90 degrees, 180 degrees, 270degrees, and 0 (or 360) degrees, for purposes of marking at thosepoints. It is further noted that the starting point for marking may ormay not be selected independent of the 90-degree rotational points, andthat the rotating portion 322 may or may not be configured so that it isnot tied to the 90-degree indexing until the scroll lock 323 is engaged.

As shown in FIGS. 20e, 20h and 20i , a keyed mating feature 331 may bedisposed at the distal end of the inner shaft 330 with respect to theoutrigger portion, for mating with a key feature 315 on the screw 10′(as shown in FIGS. 9c and 20i ), so as to locate properly the startingpoint of the measurements taken with respect to the screw, and thescroll 317. FIG. 20h illustrates a more detailed view of the distal endof the marking tool 210′, with outer shaft 333, inner shaft 330 withkeyed mating feature 331, and outrigger 324 with rounded end 338, whichtravels along the path of circle 339. FIG. 20i illustrates the measuringtool 210′, with the keyed mating feature 331 inserted into the recessedportion 303 of the screw 10′ at its fixation element 302.

Referring now to FIG. 14a , data recorded during the mapping proceduredescribed above can then be entered into a known parametric engineeringdesign software or similar algorithm, as four values, 85 a, 85 b, 85 c,and 85 d, corresponding to the four measured points, 81 a, 81 b, 82 aand 82 b, with the origin 80 defining a reference plane. These fourvalues 85 a, 85 b, 85 c and 85 d, are represented by line elements thatare geometrically constrained to lie upon a circle 90, which representsthe diameter of the measuring tool 70. These line elements are alsoconstrained to lie within planes that are perpendicular to one another.Of course, more than four points may be taken and used to map thearticular surface, e.g., 8 points; however, a minimum of four pointsshould be taken, so that two intersecting datum curves may be definedfor purposes of mapping.

Datum curves 86 and 87, representing the medial-lateral (“ML”) andanterior-posterior (“AP”) curves, are constructed by connecting the endpoints of the line elements 81 a and 81 b, and 82 a and 82 b and thepoint of origin 80, which is common to both curves. These two datumcurves 86 and 87 can be used to construct the articular or bottomsurface 41 of the prosthetic implant 40. By sweeping datum curve 87along a path defined by datum curve 86, a three dimensional surface isnow defined.

By constructing this series of geometric relationships in a knownparametric engineering model, patient-specific geometry can be input asvalues and the model algorithm can be run to reproduce the anatomiccontours mapped in the patients within only a few moments. As a process,this generic model is the starting point for all patient treatments.Sterile pins, screws, and measuring devices that are allnon-patient-specific may be stocked in the hospital and ready to usewhenever an appropriate defect is diagnosed. Patient-specific data maybe transmitted from the surgeon to the fabricating facility via aninterface to the Internet or other network. Data input into theinterface may be read directly into the generic parametric model toproduce a viewable and even mappable patient-specific parametric modelwithin moments. Confirmation by the surgeon could initiate a work orderfor the production of the patient specific device. Existing technologyallows the parametric model to generate toolpaths and programming, e.g.,to a CAD/CAM system comprising appropriate hardware and/or softwarecoupled to appropriate data-driven tools, to fabricate the implant.

Defining two additional datum curves 88 and 89, at offset distances fromdatum curves 86 and 87, is performed to define the top or non-bearingsurface 42 of the implant 40. This top surface 42 should be closelymatched to the bearing surface geometry to be implanted without havingto remove an excessive quantity of bone from the chondral surface.

Referring to FIGS. 14c and 19c , implant geometry may be defined wherebythe top or bone contacting surface 42 of the implant 40 exhibits anaxial symmetry. The central axis AA passes through the point of origin80 of the implant 40 and when the implant is positioned at the targetsite, aligns with the original reference axis 20A as defined by theguide pin 20 and fixation screw 10. The central axis AA can then be usedto define the preparation tools so that the bone contacting surfaces 42of the implant 40 and the preparation tools can be matched in bothconfiguration and dimension to create a mating fit between the surfaceof the prepared target site and the bone contacting surfaces 42 of theimplant. For example, if the preparation tools can be fabricated usingsome of the same dimensions obtained during the articular surfacemapping procedure, the implant geometry and corresponding preparationtool geometry can be mated and optimized so that a minimum verticalthickness of the implant as well as a minimum depth of bone removal isrequired. This may be advantageous in ensuring good long term clinicalresults with the implant, as poor quality of fit between bone surfacesand bone-contacting surfaces of traditional orthopedic prostheticdevices has been noted to contribute to early clinical failures.

For example, as shown in FIGS. 14c and 19c the top or bone contactingsurface 42 of the implant 40, a series of radial cuts 198 may createsurfaces that increase resistance of the implant to rotational forces.These features may be located at the outer diameter 190 of the implant40 to increase their effectiveness. Additional contact surfaces may alsobe created by one or more protrusions 195 located on the bottom 42 ofthe implant. Similarly, surface treatments known in the field oforthopedic devices, such as porous and/or osteoconductive coatings, maybe utilized on surface 42.

As shown in FIG. 19b , outer diameter 190 may include a slight outwardtaper or protrusion 197 along the diametrical surface to enhance loadbearing or load transfer properties of the implant to surrounding bone.This feature may also increase the fixation strength of the implant. Afillet 199 (as shown in FIG. 19a ) that runs around the implant at theintersection of the diametrical surface 190 and the bearing surface 41is also useful in providing a smooth transition between the hostarticular cartilage and the implant surface.

However, if a greater depth of implant is needed as a result of thedefect appearance the offset curves 88 and 89 (as shown in FIG. 14a )can be extended to increase the overall thickness of the implant 40 orthe offset curves may be eliminated entirely so that the contouredsurface is backed by a revolved geometry that is symmetrical toreference axis 20A. Turning to FIG. 19c , where the ML curve and APcurve (defined by the obtained measurements) are not axiallysymmetrical, the thickness of the implant 40 requires adjustment. At thesame time, an unnecessarily thick implant requires a greater amount ofbone to be removed at the target site. Therefore, the thickness of theimplant may be determined by taking the largest obtained measurement andadding a minimal offset amount 208. (The implant is thinnest at thehighest point on the ML curve.) This can be similarly accomplished byadjusting the angle Δ (FIG. 19a ) of the bone-contacting surface 42 ofthe implant 40 and a corresponding angle of the preparation tool. Thisalso allows for a correction of the implant geometry, to compensate forany non-perpendicular placement of the guide pin with respect to thearticular surface.

With reference now to FIGS. 25 and 26, an exemplary algorithm consistentwith the invention establishes the minimum thickness of an implantnecessary to include all patient data points, receiving as input all ofthe points measured (typically, four) and identifying the largest value.One such exemplary algorithm is as follows (and as shown in FIGS. 25 and26):

  maxval= D6  if maxval < D11   maxval = D11  endif  if maxval < D14  maxval = D14  endif D684 = maxval + .045In the foregoing exemplary algorithm, a first data point D6 is initiallyassigned as the maximum value (maxval). If . . . then type statementsare used to compare other data points (D11 and D14) to maxval. If otherdata points are greater than maxval, the algorithm reassigns maxval tothe new larger data point. LLMT represents the height of the lower limitplane along the z-axis, and ULMT represents the height of the upperlimit plane along the z-axis. D684 is a dimension that controls the ULMTplane, which is established in the model as the upper surface of theimplant. ULMT is positioned as maxval plus an additional arbitraryand/or fixed material offset (0.045 in this case).

FIGS. 5c and 5d illustrate an alternative embodiment of the implant 40′,having a ML curve between data points 340 and 341 and an AP curvebetween data points 342 and 343, with male-shaped mating component 304and key-shaped portion 344 for engagement with a reciprocal key-shapedsurface in the proximal extension of a fixation screw, protrusions 345(creating contact surfaces on the top 346 of the implant 40′), radialcuts 347 located at the outer diameter 348 of the implant 40′, andradius 349 (which may be formed, e.g. using an abrasive wheel) aroundthe intersection of the outer diameter at point 341 and the surfacecomprising the patient geometry.

Referring to FIGS. 18a and 18b , bone cutting or scoring instrument 250includes a handle (not shown), a cannulated shaft 111 that extendsthrough the handle, and offset arm 140 housing adjustable blades 141. Inthe embodiment shown, individual cutting blades 141 are attached tooffset arm 140 either fixedly or removably, e.g. via threaded portions142, into threaded recesses 342 of the offset arm 140, although otherattachment means may be used. With guide pin 20 advanced through shaft113 positioned on the reference axis 20A, a fixed distance from therotational or references axis 20A to each of the cutting or scoringblades 141 is established. These lengths define the radii that are to beeffected in the articular surface, as the scoring instrument 250 isrotated around the guide pin 20, corresponding to the protrusions 195 onthe bone contacting surface 42 of the implant 40 creating a matching fitbetween the bone surfaces of the prepared target site and the bonecontacting surfaces of the implant.

In an alternative embodiment, as shown in FIG. 18c , cutting blades arearranged on carrier 145, configured so that it can be mounted within theslotted surface 114 of offset arm 112, depicted in FIG. 17a . In anotherembodiment, as shown in FIG. 18d , cutting blades 141 can be fixedlypositioned on offset arm 140. Using the same dimensions obtained duringarticular surface mapping procedure, the cutting and scoring device 250can be fabricated to prepare the articular surface to correspond to theimplant geometry to optimize fit. In another alternative embodiment, asshown in FIG. 18e , a bone cutting instrument 352 corresponds to thealternative embodiment of the implant 40′ illustrated in FIGS. 5c and 5d. Instrument 352 has a handle (not shown), a cannulated shaft 353 thatextends through the handle and through the cannulation 355, offset arm354 with blades 350 and 351 corresponding to the protrusions 345 on thebone contacting surface 42 of the implant 40 creating a matching fitbetween the bone surfaces of the prepared target site and the bonecontacting surfaces 346 of the implant 40′.

As shown in FIG. 14b , an angular dimension 95, relating some locatingsurface or feature on the hex-shaped cover 30 or on the fixation screw10, to the four points 81 a, 81 b, 82 a and 82 b, may also be capturedat the time of the initial procedure to assist in orientation of theimplant 40 to the fixation screw 10. Guide aperture 46 in implant 40 islocated off the reference axis 20A and may serve as the locating featureand/or as a suture passage way in the implantation procedure.Alternatively, a surface or feature created on the implant 40, may serveto reference or align to such locating surface on the hex-shaped cover30 or the fixation screw 10.

Additional data can be taken at the time of the initial procedure, e.g.,for fabricating a non-circular implant. Additional data curves can alsobe defined by measuring the offsets from the reference axis 20A anddetermining diameters at these offsets. The final implant geometry,although measured using circular techniques, need not be circular.

Referring to FIGS. 10a and 10b , following fabrication of the implant40, a second procedure is performed. If a cover 30 (or plug) is inplace, it is removed, exposing proximal extension 14 (or recess) or someother precision taper or engagement surface located at the proximal end17 of the fixation screw 10 to which the implant 40 is to be affixed. Apin having a distally mounted element or barb 5 is placed throughthrough hole 16 running through the central lumen of the fixation screw10 so that the distally mounted element 5 is secured into the screw. Thedistally mounted element 5 carries one or more suture strands 85 thatnow trail from the fixation screw 10. Alternatively, a pin, braidedcable, or flexible wire may also be used. However, sutures may makepassing the implant 40 through the incision 200 and subsequent handlingeasier.

Turning to FIGS. 11a and 11b , the sutures 85 are then threaded throughguide aperture 46 of the implant 40 and a knot or bead 49 may be createdproximal to the implant, so that tensing one of the free running sutures85 helps to advance the implant 40 toward the proximal extension 14 (orrecess) of the fixation screw 10. Alternatively, the suture strands 85can be passed through the central lumen or shaft of a driving rod orother instrument to aid in seating the implant 40, and positioned in thefixation screw 10 thereafter.

If necessary, the arthroscopic wound 200 is expanded slightly in eithera vertical or horizontal direction, so that the implant 40 may be passedthrough. A polymeric sleeve (not shown) positioned over the implant mayprove helpful in passing the implant through the incision. As shown inFIG. 11b , based on the size of the implant 40, anatomy of the knee 50,and retraction of the knee, it may be necessary to position the implantin the interchondular notch 77 as a staging area prior to finalplacement. By continuing to manipulate and tension the suture strands85, the implant 40 can be brought coaxial to the proximal extension 14of the fixation screw 10.

As shown in FIGS. 15c and 15d , alternatively, driver 130 includeshandle 110, a cannulated shaft 111 that extends through the handle and acannulated seat portion 131 attached to the end of the shaft. Tetherelement 135, which may comprise sutures or wire, is passed throughdriver 130 and is threaded through implant 40 through guide aperture 46,connecting the implant to the driver toward seat portion 131. Theimplant 40 and the driver 130 are then inserted arthroscopically throughincision 200 to the target site. By tensioning tether element 135 at theend 136 of handle 110, the implant 40 is drawn back into seat portion131 of driver 130. By maintaining tension on tether element 135, theimplant 40 can then be controllably delivered to the prepared targetsite. At least the inner surface of seat portion 131 comprises amaterial that can be impacted to seat the implant 40 without damagingthe implant surface.

Referring to FIG. 12, once coaxial, the implant 40 can be aligned viaengagement of the proximal extension 14 on fixation screw 10 andprecisions taper 44 on the bottom surface 42 of the implant and anylocating feature, and driven into place with a plastic driving rod 91and mallet 95. A protrusion 92 of high strength material mounted at thedistal tip 93 of the driving rod 91 may be necessary to ensure that therod stays centered on the implant 40 during driving.

Finally, as shown in FIG. 13, through guide aperture 46 on the uppersurface 41 of the implant 40, bone cement 300 may be injected to enhancethe contact surface between the implant 40 and the subchondral bone 100.Vents, such as milled slots 13 in the fixation screw 10, and in thewalls of the implant central protrusion may be desirable to facilitatethe flow of such materials.

Alternatively, guide aperture 46 in the implant 40 may be altogethereliminated by using an alternative implant delivery system, as shown inFIGS. 19d through 19i , corresponding to an implant similar to thatshown in FIGS. 5c and 5d . The alternative system comprises the implant40″ and a washer 361 for holding a suture 363, the washer 361 beingadapted to fit into a taper lock ring 360. The ring 360 has a taper lockportion 362 having a series of notches 365 along its perimeter, creatingflaps 372 that permit the taper lock portion 362 to flex somewhat. Thetaper lock portion 362 has a diameter gradually tapering from the middleto the proximal end 364 of the ring. The taper lock ring 360 may alsohave an alignment notch 386 or similar feature for properly aligning thetaper lock ring 360 with respect to key-shaped portion 344 of theimplant 40″, which is to engage with a reciprocal key-shaped surface inthe proximal extension of a fixation screw, so as to seat properly theimplant rotationally with respect to the defect site when it is laterseated thereon. A washer 361 is disposed between the ring 360 and theimplant 40″ and has two apertures 366 disposed in a recessed area 367 inthe center of the washer. The suture 363 is threaded through the twoapertures 366 to form a suture loop 368, which remains in the recessedarea when the ends of the suture 363 are pulled, so as to keep thesuture loop 368 below the top surface 369 of the washer 361. The implant40″ has a diameter at its center portion 370 that is approximately equalto the inner diameter of the ring 360 at its taper lock portion 362.Thus, when tension is applied to the ends of the suture 363, the taperlock portion 362 of the ring 360 may flex outward to receive slidablytherein the implant 40″ and washer 361, which subsequently lock into thetaper lock portion 362 of the ring, once the center portion 370 of thesides of the implant 40″ is seated within the proximal end 364 of thering by friction fit, as shown in FIG. 19e . It is noted that the centerportion 370 of the sides of the implant 40″ to be of a width permittingthe implant and washer to travel slidably within the ring 360 to somedegree.

As shown in FIG. 19f , a hex nut 373 may be integrally formed in thecenter of the washer 361 on its bottom side 374, for mating with anappropriately configured tool for seating the implant 40″. As FIG. 19fillustrates, the implant 40″, along with washer 361, ring 360, andsutures 363, is pushed through the incision 200 at the defect site.Next, as shown in FIGS. 19g-19i , illustrative of successive steps inthe process of seating the implant, a seating tool 380 may be used toseat the implant. Seating tool 380 comprises a shaft 385, a handle 381(which may have a through hole 382, if the same handle and/or shaft isused with interchangeable tips for performing various functions,although a through hole 382 is not integral to seating the implant), andtip 383 suitably configured to drive hex nut 373 (or other matingfeature) and having an aperture 384 through which the ends of the suture363 may be threaded. Once the tip 383 of the tool 380 is introduced intothe incision 200, the sutures 363 may be used as a guide for seating thetip 383 of the tool 380 onto the hex nut 373, which may be accomplishedby alternately pulling on each end of the suture 363 to toggle the tip383 of the tool 380 back and forth. Once the tip 383 of the tool 380 isseated onto the hex nut 373, the tool 380 may be rotated in eitherdirection to seat the implant assembly properly (comprising implant 40″,taper lock ring 360, and washer 361) at the defect site. This may beeffected by rotating tool 380 until alignment notch 386 andcorresponding key-shaped portion 344 of the implant 40″ are aligned withthe corresponding reciprocal key-shaped surface in the proximalextension of the fixation screw, whereby the implant should slide intoplace, thereby properly seating the implant rotationally with respect tothe defect site. As shown in FIG. 12 with respect to the prior describedembodiment, once properly seated, the implant 40″ can be driven intoplace with a plastic driving rod 91 and mallet 95, and as shown in FIG.13 with respect to the prior described embodiment, bone cement 300 mayalso be placed prior to the final seating of the implant 40″ to enhancethe contact surface between the implant 40″ and the subchondral bone100. It should be understood that the taper lock ring 360, washer 361,and sutures 363 described with respect to this embodiment allow theimplant to be noncannulated but still easily handled. These elements arenot required to be constructed as illustrated herein, and may bereplaced by adhesive components, suction components, or other componentsserving the same function.

As FIGS. 21 and 22 illustrate, a unitary (one-piece) implant 400 mayalso be constructed, thereby obviating the need for a fixation screw,taper lock ring, washer, and suture. In this embodiment, implant 400 haskey-shaped portion 401 for engagement with a reciprocal key-shapedsurface 411 in an aperture 412 at the defect site 410, a plurality ofbarbs 402 (or other mating features, e.g., one or more threads, ribs,fins, milled slots, tapered distal features, features to preventrotational movement of the implant, or features to increase frictionbetween the implant and the aperture at the defect site) for producingoutward tension within the aperture 412 at the defect site 410 and forincreasing the contact surface area of the implant 400 with respect tothe aperture 412 at the defect site 410. In this embodiment, an aperture412 having a key-shaped surface 411 or other feature for mating with theimplant is created directly in the defect site 410, by boring, abrasion,or other techniques for forming an appropriately shaped aperture in thechondral bone 410 for receiving an implant 400 having a correspondingkey-shaped or other mating feature 401. It should also be recognizedthat, in this or other embodiments, the fixation screw could be replacedwith a tensioned member attachment, e.g., anchored to the distal femoralcortex. Alternatively, the fixation screw could be configured as a guidewire, only to define the axis AA corresponding to an axis about thepoint of origin in the implant to be used (as shown in FIGS. 14c and 19c), but not to provide mechanical anchoring to or for the implant.

FIG. 23 illustrates other alternative embodiments for an implantconsistent with the invention, showing a perspective view of thecomponents of an exemplary composite implant, in one embodiment of thepresent invention. As shown, implant 500 comprises top 501 and bottom502 portions. Top portion 501 has a bottom surface 503 which may beglued, welded, bonded, or otherwise attached to top surface 504 ofbottom portion 502, while bottom surface 505 of bottom portion 502comprises the patient geometry and is the load-bearing surface of theimplant, as set forth hereinabove. Top 504 and bottom 505 surfaces ofthe bottom portion 502 may comprise, in whole or in part, bioengineeredmaterial, while top portion 501 may comprise a material such astitanium. In such a configuration, top portion 501 may be fabricatedand/or manufactured (e.g. in large quantities) as a universal, generic,standard supply item for medical practitioners, which merely needs to beattached to a custom-machined bottom portion 502 comprising thepatient-specific geometry. Surfaces 503 and 504 may be flat or maycomprise other mating features, shapes or configurations.

Further composite implant embodiments are illustrated in FIG. 24,wherein implant 600 comprises the patient-specific geometry 603 and auniform thickness material bottom portion 602 comprising the bottom orbearing surface 606. The bottom surface 603 of top portion 601 mateswith the top surface 604 of bottom portion 602, and surfaces 603 and 604may be flat or may comprise other mating features, shapes orconfigurations. Lip 605 of bottom portion 602 has an inside diametersubstantially the same as the outside diameter of top portion 601, sothat top portion 601 fits slidably into bottom portion 602, whereby thetwo portions 601 and 602 may be glued, welded, bonded, or otherwiseattached to one another. Bottom surface 606, being of uniform thickness,reflects the patient-specific geometry which surface 603 comprises andis the load-bearing surface of the implant.

Other materials from which an implant consistent with the invention maybe constructed, in whole or in part, include ceramic, e.g. aluminumoxide or zirconium oxide; metal and metal alloys, e.g. Co—Cr—W—Ni,Co—Cr—M, CoCr alloys, CoCr Molybdenum alloys, Cr—Ni—Mn alloys, powdermetal alloys, 316L stainless steel, Ti 6Al −4V ELI; polymers, e.g.,polyurethane, polyethylene (wear resistant and cross-linked),thermoplastic elastomers; biomaterials, e.g. polycaprolactone; anddiffusion hardened materials, e.g. Ti-13-13, Zirconium and Niobium.Coatings used may include, e.g., porous coating systems onbone-contacting surfaces, hydrophilic coatings on load-bearing surfaces,hydroxyapatite coatings on bone-contacting surfaces, and tri-calciumphosphate on bone-contacting surfaces. Additionally, components of theinvention may be molded or cast, hand-fabricated, or machined.

Alternatively, measurement methods may be utilized whereby radiusmeasurements are taken with respect to an axis AA corresponding to anaxis about the point of origin in the implant to be used (as shown inFIGS. 14c and 19c ). The technique is used in reverse, whereby aimingdevices are used to place axis AA with respect to prefabricatedgeneric-geometry implants.

It is noted that, although the invention is herein described asutilizing a single reference axis, multiple reference axes may be usedfor measuring, mapping, or cutting a single defect or an articularsurface having multiple defects, as well as for fabricating a singleimplant, or multiple implants for a single articular surface, consistentwith the invention. In other embodiments, methods for mapping the defectand/or articular surface other than those described hereinabove arepossible, e.g., MRI or CT scanning, fluoroscopy, ultrasound, bonedensity, other stereotactic systems, nuclear medicine, or other sound orlight wave-based imaging methods.

It is further noted that, although the invention is described herein asutilizing the specific geometry of a patient's articular surface tofabricate an implant for that patient, it is contemplated that data froma plurality of patients may be analyzed statistically and utilized infabricating and/or manufacturing (e.g. in large quantities) one or moreuniversal, generic, or standard supply item type implants for medicalpractitioners to use in a procedure consistent with the invention. Forsuch implants, as well as for patient-specific implants as describedherein, pre- or post-implantation trimming may be required to correctfor minor variations that may occur as between the implant and thesubchondral bone (or other articular surface).

It should be understood that, although the various tools describedhereinabove, e.g., for measuring, cutting, and seating, are described asseparate devices, a single handle, shaft and/or instrument may beconfigured to serve as a universal mounting tool for a series of devicesfor performing various functions consistent with the invention.

Generic Bone Resurface Implant, Cutting Tool, and Procedure

FIGS. 27a -48 depict another exemplary embodiment of the presentinvention. In this embodiment a generic bone implant (or set ofstandardized implants) is created (or selected) based on developing anaxis normal to the surface and collecting only one data point. In theabove-described embodiments, a non-normal axis was utilized, and fourdata points were required to develop ML and AP curves. Further, ageneric cutting tool is used to cut the bone at this site to a pointwhere a generic implant can be used. Several improved tools relating tothe procedure for using such an implant (as well as for using implantsas described hereinabove) are further described in this section andillustrated in the corresponding figures.

FIG. 27a depicts an exemplary drill guide device 700 according to thisexemplary embodiment. The guide 700 includes a contact surface 702 ofknown diameter d on the distal end 708 of the guide, where diameter d isgenerally the width of the widest portion of the site of the lesion. Thedistal end 708 of the guide is generally a hollowed-out toroidalstructure attached to a handle 706. A central lumen 704 runs the lengthof the guide from the attachment point of the distal end 708 to thehandle 706, and through the handle 706. The guide device may beconstructed in a number of other ways, including, e.g., a distal end 708comprising a transparent material, e.g., polycarbonate or another clearplastic. For example, as shown in FIG. 27b , a guide device 700′ maycomprise a distal end 708′ (which could comprise either an opaque or atransparent material) having a plurality of cutaway areas 743 to improvevisibility and the accuracy of drill location with respect to the siteof a lesion. The guide device may also comprise a tripod-likeconstruction, or other construction comprising fins, or projections. Itshould be noted that, instead of a central lumen being used to locatethe working axis, a cylindrical bore located at some distal location ofthe guide may serve to create a working axis that is not necessarilycoaxial to the handle or connecting shaft of the instrument.

Referring now to FIGS. 28a and 28b , the present embodiment operates onthe assumption that to a first approximation an anatomical model of somearticular surfaces (e.g., knee, hip, etc.) can be assumed to be locallyspherical. In other words, as shown in FIGS. 28a and 28b , the AP planeand ML plane, respectively, are depicted, wherein each corresponds to amodel of the articular surface of a femoral region. These figures breakup these cross-sections into a plurality of radii of arcs defining thearticular surface, i.e., R₁-R₄ in the AP plane, and R₅-R₇ in the MLplane. In this embodiment, the inventors herein have found that surfacesin some regions can be assumed to be substantially locally spherical.Thus, for example, the present embodiment assumes that R₃ approximatelyequals R₆ (i.e., R₃ is within 50% of R₆). Under these assumptions, anormal axis can easily be developed. Once developed, one data point thenneeds to be defined to obtain the relevant geometry of an implant, aswill be described below. If R₃ is not within 50% of R₆, an alternativemethod for developing an axis normal to the surface of the lesion site,as described hereinbelow with reference to FIGS. 49-53, may be used.

FIGS. 29-34 depict the use of the drill guide, the generic implant, andprocedures therefor, according to this exemplary embodiment. In FIG. 29,the drill guide 700 is brought up to a lesion site 712 of the articularsurface 710. The guide 700 is positioned so that the distal end 702covers the lesion site 712, such that the contact surface of the distalend 702 makes contact at a plurality of points around the lesion site712 on the articular surface 710. As shown in FIG. 30, with slightpressure the guide 700 becomes stable and fixed on the articular surface710. Once seated in position, a guide pin 714 is driven through thecentral lumen of the guide to create a working axis that is generallynormal to the articular surface 710 at the point of contact of the guidepin. As FIG. 31 illustrates, a standard bore drill (not shown) can beplaced over the guide pin 714 to create a pilot hole 716 for the screw(not shown).

With reference now to FIG. 32, as with the previous embodimentsdescribed above, a screw 720 is driven into the pilot hole 716. A cap722 having a male component 719 adapted to mate with the female taper718 of the screw 720 is placed on the screw 720. The screw is driven tothe appropriate depth, such that the top surface of the cap 722 issubstantially aligned with the articular surface 710, within the lesionsite 712, thereby ensuring congruency of the implant to the joint.Turning now to FIG. 33, the cap 722 is removed, and a rod 730 having amating taper 731 on its distal tip is inserted into the screw 720. Theguide 700 is positioned over the rod 730 so that the distal end 702covers the lesion once again. As illustrated in FIG. 34, since thelength of the rod 730 and the length of the guide 700 are known, ameasurement of the exposed end length of the rod (l) may be taken. Thiswill provide the information needed with respect to the implantgeometry, by indicating the distance between the seating depth in thescrew and the tangent point of the implant surface. As shown in FIG. 35,since the axis, z, is defined (by the drill guide) as normal to thesurface of the implant at a plurality of points, all dimensions definingthe AP and ML curves may be assumed to be equal, such that only onedimension, l, is left to define the implant geometry. Variations fromknee to knee and within a knee may be reflected in changes in l. Forexample, the implant 736 of FIG. 36 may be compared to the implant 737of FIG. 37. For implant 736 of FIG. 36, the value of l₁ represents arelatively “flat” region on the articular cartilage, where the radius ofthe arc R_(AC1) is a relatively large number. However, for implant 737of FIG. 37, the value of l₂ represents a more curved region on thearticular cartilage, where the radius of the arc R_(AC2) is a smallernumber than R_(AC1). As indicated by clinical data, there is a range ofvalues for l that suggests 5 to 6 values of/that will fit a majority ofpeople. Thus, generic, off-the-shelf sized implants may be made. Asingle procedure technique involving establishing the normal axis,measuring l, and selecting the appropriate size implant is thereforefeasible.

As illustrated in FIG. 38, an exemplary cutting or reaming tool 740(e.g., as described hereinabove with respect to FIGS. 15b and 16) isused to prepare the lesion site 712 to receive the implant (not shown).The cutting or reaming tool 740 may be configured so that, when coupledto the axis defined by the guide pin, it can be used for cuttingoperations. The tool 740 may have a cannulated shaft and a distal offsetarm having a cutting or blade surface (not shown) having a radiuscorresponding to the radius of the implant to be used, such that thearticular cartilage may be circumscribed by rotation of the tool 740 forcleanly cutting the surrounding articular cartilage in preparation forreceiving the implant. The tool 740 may be configured so that, whencoupled to the axis defined by the guide pin, it can be used for cuttingoperations. The proximal face of the screw 720 may serve as a depth stopfor the proximal portion of the tool 740, thereby defining acutting/reaming depth corresponding to the thickness of the implant, l.

Those skilled in the art will recognize that the cutting tool may bemotorized in certain embodiments, and/or alternatively, as illustratedin FIG. 39, an exemplary cutting tool 744 may comprise a cannulatedshaft 749, a circular blade portion 745 having a leading edge 746comprising a blade surface turned on the distal-most portion. Such atool 744 may further comprise a handle portion 747 and may be adapted tobe turned by hand by the operator of the tool by means of rotating thehandle 747, or alternatively, may be motorized in certain embodiments.

FIG. 40 illustrates an exemplary cleaning tool 770 for cleaning thefemale taper (not shown) of the screw 720 prior to delivery of theimplant. The distal end 771 of an exemplary cleaning tool 770 comprisesa semi-rigid material formed into a shape adapted to enter into thefemale taper of the screw 720 and be manipulated by the operator of thetool, to remove tissue or other debris therefrom, thereby ensuring agood mate of the female taper 720 of the screw and the male taper of theimplant to be delivered (not shown).

FIGS. 41-43 illustrate an exemplary suction tool 760 for holding theimplant by means of a suction force and delivering it to the lesionsite, as well as the steps of an exemplary procedure for using thesuction tool 760 to deliver an implant. As illustrated in FIG. 41, anexemplary suction tool 760 comprises an elastomeric suction tip 761 atits distal portion 767, a proximal surface 768, an inlet 762 for matingwith a suction tube 763 connected either to a hospital wall suctionsupply 764 or other suction system, and a switch or valve 765 forcontrolling the suction force. As FIG. 42 illustrates, when the suctionforce at the elastomeric suction tip 761 is activated by the switch orvalve 765, the implant 742 is held in place, and thus, the suction tool760 may be used to hold the implant prior to, and during, the deliverythereof. As shown in the cross-sectional view of FIG. 43, the distalportion 767 of an exemplary suction tool 760 may comprise a rigid tip766 (which may comprise, e.g., plastic material) disposed within theelastomeric suction tip 761. Force may be applied to the rigid tip 766(e.g., by striking or pressing on the proximal surface 768 of the tool760) in order to seat the implant 742 within the lesion site, once themale taper 769 of the implant 742 and its corresponding matingcomponent(s) 778 are properly aligned with the female taper of the screw(not shown) and its corresponding mating component(s). Since the suctiontip 761 is elastomeric (e.g., rubber), upon application of such force,the material will compress, allowing impact to be transferred to theimplant 742 for purposes of seating it. It is noted that, in addition toits utility in delivering an implant, a suction tool 760 as describedherein (or a suction tool similar thereto) might also be used at somepoint during the process of removing an implant (e.g., in the event theimplant is not fully seated).

FIG. 44 illustrates an exemplary implant 742 driven into the lesion site712 of the articular surface 710 once the site 712 has been sufficientlyreamed or cut.

FIG. 45 illustrates an exemplary implant removal or revision tool 750comprising a shaft portion 751 and a distal portion 753, and FIG. 46 isa cross-sectional view illustrating the exemplary tool 750 with aremoved implant 742 being held in place therein. As shown, the distalportion 753 of the tool 750 may comprise an approximately cylindricalstructure with a circular blade portion 752 having a leading edge 758comprising a blade surface turned on the distal-most portion and a lipportion 755 disposed proximally with respect to the leading edge 758. Aplurality of slits 754 parallel to the longitudinal central axis of thedistal portion 753 are disposed along the length of the cylindricalstructure, so as to permit sufficient outward expansion of the distalportion 753 to accommodate the top edge of the implant 742 therein.Thus, when the distal portion 753 of the tool 750 is forced onto animplant 742 to be removed, and driven down over the implant 742, thedistal portion 753 will snap/lock into place once the lip portion 755 ofthe distal portion 753 of the tool 750 passes the top edge of theimplant 742 being removed, thereby holding the implant 742 in placewithin the distal portion 753 of the tool 750, as shown in FIG. 46. Atthis point, a device such as a slap-hammer or slide hammer (not shown)may be used to unseat the implant 742. An exemplary such device maycomprise a shaft having a weight slidably disposed thereon, wherein oneend of the shaft is connected to the proximal end (not shown) of thetool 750 and the other end of the shaft comprises a stop for preventingthe weight from moving off the shaft, and wherein the weight ispropelled away from its connection point with the proximal end of thetool 750, such that it stops abruptly at the stop and exerts a pullingforce on the implant.

Alternative Embodiment of Screw

FIGS. 47 and 48 illustrate an exemplary alternatively-keyed embodimentof the screw 720′ (c.f., key feature 315 of screw 10′, as shown in FIG.9c ) and the exemplary alternatively-keyed implant 742′ to which it isadapted to mate. As shown, the male taper 769′ of the implant 742′ iscoupled at its distal end to an offset mating feature 778′ for matingwith a corresponding offset mating feature 779 of the screw 720′. Themating feature 778′ of the implant 742′ comprises a generallycylindrical structure (and may further comprise a rounded or chamfereddistal end portion 777′ and/or other geometric features, i.e., recessesand/or protrusions) and is both offset from the central longitudinalaxis of, and diametrically smaller than, the male taper 769′ of theimplant 742′. As FIG. 48 illustrates, a generally cylindrical recessedmating feature 779 (or similar mating recess(es) and/or protrusion(s),e.g., a rounded or chamfered distal end portion 780) corresponding tothe offset distal mating feature 778′ of the implant 742′ is disposedwithin the innermost portion of the female taper 718′ of the implant742′, and offset from the central longitudinal axis of the female taper718′. The female mating feature 779 of the screw is provided to matewith the offset male distal mating feature 778′ of the implant 742′, soas to seat the taper 769′ of the implant 742′ at a fixed location withinthe screw 720′, thereby preventing rotation of the implant 742′ withrespect to the screw 720′. Along with the mating features 778′, 779, thetaper structures provided may serve to prevent movement of the implant742′ with respect to the screw 720′ in all directions. A screw 720′consistent with the present invention may comprise a titanium alloy,e.g., a 316L stainless steel alloy or a cobalt-chrome alloy.

Alternative Method for Developing Axis Normal to Lesion Site Surface

FIGS. 49-53 illustrate an alternative method for developing an axisnormal to the surface of the lesion site using a biaxial measuring tool.This method has particular utility for lesion sites where the radii ofarcs defining the articular surface, R_(ML) and R_(AP), are different,i.e., the region is not locally spherical. (This would be the case,e.g., if R₃ is not within 50% of R₆, as illustrated in FIGS. 29a and 29band described hereinabove.) To develop an axis normal to the surface, abiaxial measuring tool 800 is provided. The tool 800 comprises an outershaft 805 coupled fixedly to an outer component 801 having a set of arms803, and an inner shaft 806 slidably disposed within the outer shaft805, wherein the inner shaft is coupled fixedly to an inner component802 having a set of arms 804. The arms 803, 804 of the outer 801 andinner 802 components may take several forms, and one exemplary form forthe arms 803, 804 is illustrated in FIGS. 49-53, wherein the distalportion of each arm 803, 804 tapers outward and connects to one of fourcontact portions 808. The contact portions 808 may be, e.g., as shown,one of four arcuate sections of a generally toroidal member (which maybe solid or hollow) having a generally circular cross-section. (Thelengths of the arcuate sections do not necessarily need to be equal toone another, e.g., as illustrated in the exemplary contact portions 808of FIGS. 49-53, the arcuate lengths of the contact portions 808corresponding to the inner component 802 are shorter than those contactportions 808 corresponding to the outer component 801.) The inner shaft806 may be biased forward so as to tend to extend from the outer shaft805, or may alternatively be advanced manually without spring bias. Theinner component 802 is slid proximally or distally with respect to theouter component 801, until all of the contact portions 808 make contactwith the articular surface (not shown). In this manner, the articularsurface curvatures may be separated into AP elements and ML elements,such that four separate contact points may be extrapolated from the fourcontact portions 808, based on the relative positions of the inner 802and outer 801 components, and an axis normal to the surface of thelesion site may be defined. The shaft of the tool 800 may be cannulated(not shown), so as to allow a guide pin or wire (or a boring tool) topass therethrough and into the articular surface, as describedhereinabove with respect to FIGS. 27a to 31. As shown in FIG. 53, if theinner 802 and outer 801 components are aligned such that the fourcontact portions 808 meet to form a complete toroidal member or ring,the articular surface must be locally spherical, i.e., R_(ML) and R_(AP)(as shown in FIG. 49) are equal, and it is therefore not necessary touse the biaxial tool 800.

It should be noted that, alternatively, contact surfaces may beconstructed of some pliable, or malleable material(s) so thatindependently moving rigid mechanical members are not necessary. As longas the contact surfaces provide a normalizing force to some centralshaft when the contact surfaces are applied to the articular surface, anormal axis could be defined.

In another embodiment, this biaxial guide could be replaced by a seriesof sized “trials” or gauges of predefined surfaces of varyingdimensions, which are simply pressed onto the articular surface tovisually determine an appropriate fit. These gauges may resemble animplant, as described herein, without any features (e.g., fixationelement or screw) on the underside, and may contain a handling tab orother element for holding the gauge. The contact surfaces of thesegauges may have a circular cross section, an ovular cross section, oranother cross-section comprising a plurality of points to surround adefect in an articular surface, and the plurality of points may or maynot lie in the same plane. Although they may be less precise or lessaccurate than other measuring methods described herein, it iscontemplated that implant selection could be made directly from thesegauges.

Digital Measuring System

FIGS. 54-61 illustrate an exemplary digital measuring system consistentwith the present invention. As shown, the system 810 comprises a baseunit 811 coupled to the handpiece 812 via a cable 813. As describedfurther hereinbelow, the base unit 811 may comprise a tear strip 814 inor on the chassis for detaching a printed paper tape comprisingmeasurement data. Such a system may reduce or eliminate potential forsurgical or other human error with respect to the implementation of thepresent invention.

FIG. 55 is an exploded view of an exemplary handpiece 812 in a digitalsystem consistent with the present invention. The linear measuringelements of the handpiece 812 are nested concentrically and coaxially tothe rotary measuring elements, so that when the probe assembly 818 istranslated and rotated with respect to the main body 822 of thehandpiece, the θ and z dimensions are simultaneously recorded. Thehandpiece 812 comprises a main body 822 containing a linear reading head813 coupled to a linear reader 814, a linear index strip 815, a rotaryreading head 821 coupled to a rotary reader 816, and a rotary indexstrip 817. The probe assembly 818 comprises a contact tip 819 coupled toan inner shaft 820 running along the length of the handpiece 813disposed within the main body 822. The shaft 820 comprises a matingfeature 834 at its distal end that is keyed to fit in the mating featureof an implanted screw, such that the shaft 820 provides a rotationalaxis. The shaft 820 is rigidly connected to the main body 822 of thehandpiece 812 via a nut 823 at its rear. The handpiece 813 is coupledto, and transfers motion both rotationally and axially from, the contacttip 819 via the shaft 820. In this manner, the linear 815 and rotary 817strips, which may comprise, e.g., mylar polyester film having thereon avery fine printed pattern, pass through the linear 813 and rotary 821reading heads, respectively, such that the heads 813, 821 read thepattern on the strips 815, 817 and output data representing therotational and axial travel of the contact tip 819.

Exemplary strips and heads may include those manufactured by U.S.Digital™ Corporation of Vancouver, Wash., USA. FIG. 55a is a cutawayview illustrating an exemplary printed linear index strip 815 passingthrough an exemplary linear head 813 for reading, and FIG. 55b is acutaway view illustrating two alternative exemplary printed rotary indexstrips 817, 817′ of varying sizes passing through an exemplary rotaryhead 821 for reading. FIG. 55c illustrates an exemplary linear indexstrip 815 comprising concentric “bullseye” circles 830, reference lines831, a text area 832, and a pattern area 833. FIG. 55d illustrates anexemplary rotary index strip 817 comprising an opaque area 823, indexareas 824, a pattern area 825, a text area 826, crosshairs 827,concentric “bullseye” circles 828 and a central aperture 829.

Turning now to FIGS. 56a and 56b , a rotational groove 840 and a lineargroove 841 are provided on the handpiece 812, such that the probeassembly 818 may slide onto the shaft 820 of the handpiece 812 and snapinto the linear 841 and rotational 840 grooves.

FIGS. 57 and 58 illustrate top and side views, respectively, of theassembled exemplary handpiece 812.

FIGS. 59 and 60 illustrate top and side cross-sectional views,respectively, of the assembled exemplary handpiece 812.

FIG. 61 illustrates a cutaway view of an exemplary base unit 811 in anexemplary digital measuring system consistent with the presentinvention. The base unit 811 comprises a power supply 850 (the systemmay be battery or AC-line powered), a paper roll 851, a thermal printer852, a feed loop dowel 853 for threading the paper roll 851 into thethermal printer 852, a set of controls or buttons 854, and one or moredisplays 855 (e.g., LED/LCD). The base unit 811 further comprisesappropriate hardware and/or software to compare measured values to knownvalues, as well as to compare sweeps to one another to ensure proceduralaccuracy. Further, the displays 855 and/or paper printouts from thethermal printer 852 may be adapted to display to the user, based onmeasured data, the ideal size of the generic implant to use. If a customimplant is required, a printout of the data set may be generated usingthe printer 852. The base unit 811 may further comprise other means ofrecording data (not shown), e.g., floppy disk, hard disk, memory/flashcard, etc., and may further comprise appropriate hardware to provideoutput signals (e.g., via RS-232, USB, etc.) to external hardware.Instead of the strips, heads, and other recording elements described inthe exemplary digital system hereinabove, other digital measurementmethods may be used, including reflective light or sound methods, andpercutaneous methods (e.g., using a hypodermic needle in conjunctionwith an MRI, CT, ultrasound, or other scanning method, wherein theneedle or other handheld device comprises sensing elements for mappingthe articular surface).

It should be noted that in the digital measuring system and methoddescribed hereinabove (as well as any of the mapping/measuringtechniques herein), a second (or third, etc.) set of data points may betaken, and the subsequent set(s) of data points compared with theoriginal data points taken, to reduce the margin of error from takingonly a single set of data points. Thus, a software algorithm in a systemor method consistent with the invention may comprise appropriateroutines to effect such comparisons, for error reduction purposes.

Those skilled in the art will recognize that the present invention issubject to other modifications and/or alterations, all of which aredeemed within the scope of the present invention, as defined in thehereinafter appended claims.

What is claimed is:
 1. A guide device for locating a working axis, saiddevice comprising: a cannulated outer shaft having two coaxial openingsat generally opposite ends thereof; and a cannulated inner shaft havingat least a portion configured to be slideably disposed within at least aportion of the cannulated outer shaft, the inner shaft defining a shaftlumen extending along a longitudinal axis of said cannulated inner shaftand having two coaxial openings at opposite ends of the cannulated innershaft; wherein a distal end region of at least said cannulated outershaft includes a contact region configured to contact with an articularsurface to generally align said longitudinal axis of said cannulatedinner shaft substantially normal to a first and second curvature of saidarticular surface.
 2. The guide device of claim 1, wherein the outershaft further comprises an outer component coupled fixedly to the distalend region of the outer shaft, the outer component including a first setof arms tapering outwardly, wherein a distal portion of each of thefirst set of arms connects to a respective one of a first pair ofcontact portions; and wherein the inner shaft further comprises an innercomponent coupled fixedly to a distal end region of the inner shaft, theinner component including a second set of arms tapering outwardly,wherein a distal portion of each of the second set of arms connects to arespective one of a second pair of contact portions.
 3. The guide deviceof claim 2, wherein at least one of the first and second pairs ofcontact portions comprises an arcuate section of a generally toroidalmember.
 4. The guide device of claim 3, wherein the first and the secondpairs of contact portions comprise arcuate sections.
 5. The guide deviceof claim 4, wherein the arcuate sections have equal lengths.
 6. Theguide device of claim 4, wherein the arcuate sections have unequallengths.
 7. The guide device of claim 6, wherein the arcuate lengths ofthe first pair of contact portions are shorter than the arcuate lengthsof the second pair of contact portions.
 8. The guide device of claim 1,wherein the inner shaft is biased forward so as to tend to extend from adistal end region of the outer shaft.
 9. The guide device of claim 1,wherein the inner shaft is configured to be advanced manually withoutspring bias.
 10. The guide device of claim 1, wherein a distal endregion of the cannulated inner shaft further includes a contact regionconfigured to contact with said articular surface to generally alignsaid longitudinal axis of said cannulated inner shaft substantiallynormal to said first and said second curvature of said articularsurface.
 11. The guide device of claim 1, wherein said contact region isfixedly coupled to said distal end region of said outer shaft.
 12. Theguide device of claim 1, further comprising a shaft having a tipconfigured to be advanced through said coaxial openings of saidcannulated inner and said cannulated outer shafts and into the bone. 13.The guide device of claim 12, wherein said shaft comprises a guide pininclude a threaded tip configured bore into the bone.
 14. A method forestablishing an axis substantially normal to a portion of an articularsurface of bone generally defined by a first and a second curvature,said method comprising: obtaining a guide device comprising a cannulatedouter shaft and a cannulated inner shaft, wherein said cannulated outershaft comprises two coaxial openings and an end region including acontact region, and wherein said cannulated inner shaft defines a shaftlumen extending along a longitudinal axis of said cannulated inner shaftand having a two coaxial openings; advancing said end region of saidcannulated outer shaft against said articular surface and advancing atleast a portion of said cannulated inner shaft within at least a portionof said cannulated outer shaft such that said longitudinal axis of saidcannulated inner shaft is aligned substantially normal to said first andsecond curvature, respectively, of said articular surface; and advancinga shaft having a cutting tip through first and said second openings ofsaid shaft lumen the cannulated inner shaft and into the bone along theaxis.
 15. The method of claim 14, further comprising excising at least aportion of the articular surface radially symmetrically about the axis.16. The method of claim 15, wherein excising the articular surfacecomprises rotating a cutting tool about the axis.
 17. A system forestablishing a working axis substantially normal to a portion of anarticular surface of bone, the system comprising: a guide devicecomprising: an outer shaft defining an inner shaft lumen having twocoaxial openings at generally opposite ends thereof, said outer shaftfurther comprising a contact region configured to contact the articularsurface; and an inner shaft slideably disposed within said inner shaftlumen of the outer shaft, the inner shaft defining a shaft lumenextending along a longitudinal axis of inner shaft and having a firstand second coaxial opening; and a shaft including a tip configured to beadvanced through said openings of said inner shaft lumen and said shaftlumen and into the bone beneath the articular surface, said shaft havinga length greater than a length of said guide device.
 18. The system ofclaim 17, wherein said shaft includes a guide pin include a threaded tipconfigured bore into the bone.
 19. The system of claim 17, furthercomprising an excision device configured to be advanced over and rotatedaround the shaft extending from the bone to establish an excision sitein the articular surface.
 20. The system of claim 19, further comprisingan implant configured to be received in the excision site, said implanthaving a curvature substantially corresponding to a contour of theremoved portion of the articular surface.